Crikey @Anonymous User, you seem to be having more than enough problems with this one and I'm sorry about that. @schnapps has been brilliant and has suggested everything that i would have done so all I can do is to give you some kind of checklist.
1) Do you live in a good TV reception area? (Don't answer that as I don't want to know where you live 
) Check your neighbours, have they got big aerials visible ?
2) Maybe you can't see an aerial on a neighbour's house or live in the countryside, many new houses don't allow an external aerial and if you live out in the wilds of this lovely country of ours ("Escape to the Country" envy from this end!) Then you might have problems with a "Straight line" signal from a transmitter. An example of this is that, not far from me, in West Yorkshire, one area has to pick up it's signal from what used to be called "Tyne Tees", even though there is a stonking great transmitter for "Yorkshire TV" at Emley Moor, 10 miles away!
3) Have you stored something in the loft recently that might interfere with the signal (An old Microvave or something metal) or has some building work happened around you lately that might impede the signal that you had?
4) You have already mentioned this but try it again, please......If you plug your aerial straight into your TV do you get any more Freeview channels than through your NOW TV Box? If you do, there might be a need for a reset on your NowTV Box, if you don't then it's down to signal strength and you have an aerial problem. The number of channels that you say that you receive, suggests (As @schnapps rightly says) that you're in a poor reception area.
5) Broadband strength....How are you doing with that? NowTV, is , at heart a "Catch Up" and "On Demand" service and relies in a decent/good broadband speed and again, if you are out in the countryside, you might suffer lower speeds than many of us. (That is only for "Catch Up", not "LiveTV")
6) That's about it but I have to second @schnapps advice that before your other half steps into the attic....Tell him to watch his step! In this day of Digital TV if you can get a signal then it is good or bad (Picture on the telly or none at all) so a slight adjustment won't work...Sorry, but tell him (In my opinion) not to bother.
7) Finally (Hurrah!) I think that the answer to your problems might be a "High Gain" aerial, professionally fitted by a local expert, who will have probably come across the problems that you are experiencing, and cure them for about the £80-£100 mark.....Not pleasant, I know.
I'm sorry that I can't be of more help but I really hope that you get the problem sorted and can enjoy some telly again.
Good luck and all the best! 
Sound advice again @schnapps and a couple of nice little tips in there as well, thanks for those.
@Anonymous User, If you can check on your neighbours aerials, a "normal" aerial for a good reception area would be a Perforated aluminium plate, or a series of rods at the back (That's the Reflector) with a bar sticking out in front. On that bar will be a series of 8 rods mounted across it, either horizantally or vertically, depending on the area that you live in (They are the Elements).
If your neighbours have longer aerials, they will have 16 elements on them and it's a sign that you are in a poor reception area. The next step is that if those neighbours have aerials with the elements forming a series of "X" patterns along the length, then they have high gain or extra gain aerials and that is a sure sign that you need more signal strength in your area.
High gain aerials, again come in 8 element (XG8...XG for Extra Gain and 8 for the number of elements) 12 elements (XG12) and 16 elements (XG16).....To be honest, if I lived on the Isle of Skye, I would expect to pick up a good signal from North Wales with an XG16!!!!!! If the mast was high enough to see over the horizon I bet you could, that's how much signal they bring in. The downside is that they are expensive, even an XG8 will tip you over the £100 mark to have fitted.
Sorry that I've still not come up with some whizzy answer that will cure your problem but I hope that you can get it sorted, soon.
All the best.
Just a final (I promise!) note on the aerial thing @Anonymous User is that if your other half is a handy lad and takes every precaution when he ventures into the loft you can actually fit an aerial yourselves. A few quick photos on your phone to check the direction (Alignment) of your existing aerial and the connection arrangement from the co-axial cable (Aerial lead with 2 connections...A solid inner, copper wire and a braided mesh outer wire...Make sure that they are not touching each other!!!!)) and you can fit one of these:
It's not as difficult to fit as it was back in the "Analogue TV" days, when you could get "Ghosting" and other problems. These days, as I said before, with digital you get a picture on your telly or none at all, so a few shouts through the loft hatch with you looking at the TV and your other half lining up the aerial should do the trick. You can't do any damage as there is no electricity, it's just a signal......I say you can't do any damage, if you hear a shout and you see your Hubby's leg sticking through your bedroom ceiling, then things have gone a tad wrong!
Like I say, a few photos to check on and a whole bunch of care should sort you out.
Take care and good luck.
PACKED WITH FEATURES TO IMPROVE RECEPTION OF DIGITAL TV FULL RANGE FOR LOCAL THROUGH TO FRINGE RECEPTION AREAS UNIQUE DESIGN INCREASES SIGNAL STRENGTH MASSIVE REFLECTOR REDUCES NOISE PICK-UP
A-Ha! @Anonymous User......It's those pesky trees wot did it!
If you have enough trees around to block the line of sight to the satellite, you will also have problems with your aerial getting enough signal from the transmitter. That will be made worse by the fact that your aerial is in the loft, rather than outside as the structure of your roof will reduce the signal. Back to the trees and you will find that your reception is worse in the summer, when leaves are on them, than in winter.
You can get and fit/have fitted an extra gain aerial and that will help, at a cost but even then it might not actually cure the problem, depending on how thick the trees are.
To be honest, I think that if you have a good broadband speed, you should follow the great advice from @schnapps and use the NowTV box to watch "Sky" programmes on catch up and watch live shows via IPlayer for the Beeb and the various players for the other channels.....At a guess, the way that TV is developing at the moment, I think that reception through an aerial will be a thing of the past, in a few years as more and more of us migrate to a broadband delivery of our telly programmes.
I'm not surprised that it's taken a while for you to get back to us.....The weather has been absolutely cracking, hasn't it.....8pm and it's still 26 degrees up here.....Us Yorkshire Tykes think that the West Riding has been twinned with Mercury!
All the best.
