The different BIOS steps are not displayed on the screen any more: no BIOS parameter setup option, no Windows boot option (we set a waiting period of 15 seconds).
We ran a Passmark BurnInTest and the only failure pointed out was a defective NVIDIA GEForce PCX 5300 graphic card. Driver is recent (May 2008, vers. 126.96.36.19919). XP Control Panel Device Manager indicates that the driver is working fine.
PC is 4 years old.