FREEEZING

okay so when I boot up my computer with in 3 - 5 minutes my computer freezes...I am not talking about Freeze for a second then keep going. I am talking about everything freezes mouse wont move task manager wont come up or anything. I left it like that one time it happend to see if it would ever start working again and no. I have to manually unplug it to get it to work all the usb stops responding and everything. I thought it might be over heating so I took every thing apart and blew it out with air. didn't help I put a box fan on low and let it blow in it to keep it cool to see if that would help no. I am currently in Safe mode and it seems to be not freezing I ran a virus scan three times and nothing has shown up. And since I was starting up in safe mode and it wasnt freezing like normal I thought maybe I could do a system restore and that would fix it.. no. I am completely at a loss here. Does anyone know what is going on?

OS Name Microsoft Windows XP Professional
Version 5.1.2600 Service Pack 3 Build 2600
OS Manufacturer Microsoft Corporation
System Name OWNER-67P7ZEE2I
System Manufacturer Dell Computer Corporation
System Model OptiPlex GX270
System Type X86-based PC
Processor x86 Family 15 Model 3 Stepping 4 GenuineIntel ~2394 Mhz
BIOS Version/Date Dell Computer Corporation A06, 9/29/2004
SMBIOS Version 2.3
Windows Directory C:\WINDOWS
System Directory C:\WINDOWS\system32
Boot Device \Device\HarddiskVolume1
Locale United States
Hardware Abstraction Layer Version = "5.1.2600.5512 (xpsp.080413-2111)"
User Name OWNER-67P7ZEE2I\Administrator
Time Zone Central Daylight Time
Total Physical Memory 896.00 MB
Available Physical Memory 571.14 MB
Total Virtual Memory 2.00 GB
Available Virtual Memory 1.96 GB
Page File Space 1.55 GB
Page File C:\pagefile.sys