Windows wont boot

hey guys i fixed my power supply problem (i replaced my 450w max Power Supply with a 300w max one i found lying in my garage)but now whenever i try and boot to windows, the system automatically reboots right at the windows loading screen and i cant log in safe mode either....WTFUX?!

1. Boot the computer, but instead of booting the OS, go into the BIOS.
2. Keep it sitting there at the BIOS screen for about an hour.

If the system can't sustain itself on the 300V supply, you'll find out in that fashion.