Hi Leocrux. The first thing you can do is to run some hardware diagnostics yourself. The obvious concerns would be the hard drive, and the memory.
Testing for Hardware Failures (Windows 7, Vista)
If that passes, I have included a document explaining several ways to put the computer back to factory defaults. Also there is the troubleshooting document if those recovery methods do not work.
Performing an HP System Recovery (Windows 7)
Troubleshooting HP System Recovery Problems (Windows 7)
I hope this helps.