WinXP boots to Safemode but stalls at XP splashscreen

Hi,

I've been battling my computer all day. First of all for the basics its an HP windows Media machine with 2 dual 1.5g processors and 2g of ram, and a 256m video, 300g hd and dvd/cd burner. This machine was running fine for the past couple years. I started shutting it off at night 2 nights ago and rebooting in the morning. It worked fine for the first few days, and again today it booted just fine. Then I shut it down today after playing a game on it for a while, but this time when I booted it stalls at the winXP splash screen with the progress bar constantly running across. I can reboot the machine in safe mode with no problem, and I was even able to launch the game I played earlier today in safemode (didn't know that was possible). I shut down and rebooted, but again it stalls at the splash screen. I've tried running checkdisk /p from a command prompt before windows boots but it stalls at 19%. I boot into safemode and try running checkdisk from My computer but it stalls at 79% on the first pass. I've checked the event viewer and there is nothing there. Looked at device manager (all this from safe mode) and it lists no devices, nothing. I've checked the cmos settings and my times are upto date. I've left the winXP splash screen up and running to see if it will eventually force its way in but i'm not hopefull. While in safemode I've gone into msconfig and turned everything off and tried booting, but again nothing. Not sure where else to go from here. Can someone please help. I've been running AVG and just did a virus scan 2 days ago and nothing came up. Not sure where else to go from here. Does anyone have a suggestion as to what I should do now.

Download, update & run anti malware from malwarebytes.org

Ran Malwarebytes from safe mode, it completed then the whole computer stopped responding. Rebooted again and ran virus scan, it completed, but ran in a command prompt mode. When it completed the computer locked up again, rebooted again and went into restore mode. Ran a hardware analysis and it found a hd problem and gave me the error code HD521-2VV. Researched the code but couldn't find much on it about how to fix it or if possible. backed up my data I wanted to keep and tried an os restore. This didn't help, went back to doing the exact same thing. Completed a complete destructive restoral to new status. This worked for a while, now I can boot it and it gets to the login window to choose which user to log in. The mouse moves around the screen but cannot click on any of the users. Before it stopped responding I started reinstalling software again. I removed all the crap that comes with the machine, and installed Office 07 and the latest version of Radeon ATI Catalyst. As soon as it was installed and rebooted this started happening. I didn't install it before this happened in the beggining. I'm going to uninstall Catalyst from safemode if I can get to it, and see what that does. Any thoughts from anyone on what else I could do.

If you had a hard drive error, then you need to download the diagnostic tools from the manufacturer of the hard drive. There could be some bad blocks & those tools will confirm that.

Do you know what make HD is in the PC?