System will fail to boot up after periods of inactivity

Early December I ordered a new motherboard, ram, hard drive and cpu.

Motherboard: Gigabyte 890GPA-UD3H
CPU: Phenom II 1090T
Ram: Mushkin 4gb 2x2GB 8-8-8-24 Blackline kit
Hard Drive: Samsung F3 1TB

I installed windows 7 no problem, installed up to date drivers for everything etc etc but I would find that if I didnt use the computer for some time, say 10hours+, when I went to boot up windows would not load. It would try to take me to startup repair, which would sometimes work, sometimes not, usually removing 1 stick of ram would some how make it work then I could put the other back in and all is fine. There really was a pattern with this, if I didn't have time to turn on my computer before work for 5minutes, I knew that when I got home, cause it hadnt been on for say 15hours windows would not load so i'd need to restore. This only worked sometimes by the way, other times i'd just get black screens with a curser etc.

I have reinstalled Windows many times, I'd say about 10 since having these components, on different hard disks, with 1 ram stick, with default ram settings, or ram settings found off the mushkin website, with and without my Soundblaster x-fi titanium card in, nothing seems to work. When installed and working, everything seems fine. Then the next day when it hasn't been in use for some time, not fine.

I have run numerous stress tests to check for errors, prime95 doing the full system test, all 6 cores purring away at 100% for hours and no errors, memory tests for hours and no errors, disk error checks and nothing, it really makes no sense to me. How could I say, leave it working it's nuts off for 24hours solid and there's not a single problem, then turn it off, leave it 12hours, turn it on and it can't even manage to boot up? Infact now the problem is more frequent and it doesn't seem to need these big downtime periods to decide to break, just a couple of hours is dodgey.

I have just finished my 2nd Windows 7 install of the year so far and to say the least it's a little tedious, I could try and RMA the odd component back but as I say at first all works fine, I think they'd have trouble replicating the issue.