I just built a new computer myself, it was my first build. It has been having problems booting into windows but only the first time, other times it boots into it fine. I've just been putting the computer to sleep to avoid this problem.
The Specs are:
Asus P7P55D-E motherboard
G.Skill 1600 Memory
I ran memtest and got thousands of errors, so i got the memory replaced. That didn't help at all, so i got the motherboard replaced, again this didn't help.
My dad and the IT guy at his work had a look at it and both concluded it would probably be the Graphics card, so I borrowed the IT guys card to test it and still no result. It actually got worse and now to get it not to blue screen i have to remove a stick of RAM after the first one and reboot.
I am almost out of ideas, the next thing I will try is to get another hard drive and try out XP with it (I've got 7 install atm).
There are absolutely no problems aside from this, it plays games excellently and doesn't crash any other times.