Problems with PC starting

Hi, now and then my PC fails to restart. I've been checking BIOS settings and changing booting orders, etc, but didn't help.

It comes to the part
PCI Devices Listing...
-------- some listings
and stops at "ACPI Controller" with IRQ 9

It is not frozen, because Alt-Ctr-Del 1 time easily restarts it, but not other thing i tried seems to work.

Finally, when I disconnected today my external drive, it restarted. But I had this before I bought the drive (actually i bought the external worrying about data)

I got Maxtor so i downloaded their diagnostics tools for hard drive and it said all is ok.

I also noticed this happening when I leave the PC on for some days or overnight (i usually dont switch it off) and in some cases it restarted after few hours of "rest", i.e. turned off.


I hope someone can help, because since i can't reproduce it, I can't get the PC shop to help...

THANKS A LOT!!!


Some info:
running XP, pentium 4 2.40Hz, 1 GB RAM, disk drives are Maxtor 6L200P0 and 6V160E0 (dont know which is the C drive), got 5 fans for cooling as had overheating problem before. ok, tell me what else i dont know.

 

Thanks a lot.
After some time I caught this error. It came on a blue screen with white letters.

"<bla bla bla>
Technical info:
STOP: 0X0000008E (0xC0000005, OXBFOBFEAC, OXF1201C10, 0x00000000)

nv4_disp.dll - Address BFOBFEAC base at BFO12000, Datestamp 411096d7

Beginning dump of physical memory
Physical memory dump complete
Contact system administrator bla bla"

Other info:
- This is my PC, I am the "admin".
- This happened during playing a 3D game (about 2-3 hours after start)
- Previous shutdowns usually happened when I left PC on overnight for download or other and I was not present.


---------------
Thank you very much for your help.
I would appreciate a short explanation so I can fix things myself in the future.
THANKS!