Can you elaborate a little bit more on your system, hardware, please ?
Can you boot into Safe Mode ?
Have you done a diagnostic test on your memory by booting to a CD created with memtest86+, a copy of which can be found at http://www.memtest.org/
Other than that, do you have any BSOD codes to post ? If not, before booting to Win 7, please press F8 to boot into Windows Advanced Boot Options. Here choose to turn off Automatically Reboot feature. Then boot normally. This will give you the chance to see any BSOD codes.
Hope this helps.