System freezes or takes a long time to boot

I am having a lot of problems booting my computer (in sig). It will get to the starting windows screen, and just hang there for anywhere from 3 min to days. I cannot find a pattern as to how long it will take. Rebooting often does little to alleviate the problem. When it does boot, I can leave it running for weeks without a single problem or instability. I have been very busy with school and traveling so I have yet to get a chance to try a full blown reinstall. Any other diagnostic ideas or thoughts as to what is causing the problem?

Windows 7 64bit, all hardware at stock speeds

Thanks in advance!

Is anything you installed to blame? See what is starting up at boot using this freeware:
http://www.nirsoft.net/utils/what_run_in_startup.html

After that, disconnect everything connected to your machine and take out extra cards you may have so that only ram and video card are left basically, to see if any piece of extra hardware is the culprit, especially tv cards and sound cards etc.