When you state that the reboot crashes, what do you mean specifically? Are you seeing a BSOD (blue screen of death) along with an error code? Or perhaps your Windows 7 is configured to reboot automatically after a BSOD, making it harder to note the error that caused the crash.
First things first: If your system is stable enough to use, check your error handling options by bringing up the ADVANCED SYSTEM SETTINGS window as follows:
1) Hit the WIN key and PAUSE BREAK to bring up system settings (alternately you can click the START orb, right click on COMPUTER, and choose PROPERTIES). Once there, click on the advanced system settings link on the left: Attachment 35126
2) When that appears, click the Advanced tab, then the SETTINGS button: Attachment 35127
3) Deselect the "Automatically Restart" checkbox and change the debugging information to "Small Memory Dump" as seen here: Attachment 35128
Assuming you are in fact encountering a BSOD this change will allow the blue screen error to remain on your screen, giving you the opportunity to copy down the error code you see so that you can then post it here.