Operating system: Windows XP Media Center
AMD Athlon 64 X2 Dual Processor

I spent all night working on my computer (yeah, I didn't sleep). In the morning, while I was editing some graphics in Photoshop CS3, my PC froze but I wasn't able to close the program nor restart so I just shut down the computer by pressing the power button. When it restarted I was unable to get past the "windows is starting up" screen. It freezes right there. Even the mouse pointer freezes.

Does anybody have any idea of what may be wrong? I have a lot of work to complete and I'm hoping it's not a software issue because I don't want to lose my data. Please help me guys.