Dead motherboard battery (probably not as that would cause a loss of CAMOS settings but you should still get something on boot attempt), Power supply (could be but check connection to motherboard and all hardware), Motherboard, video card, dead monitor. Of these problems, I have had the: dead motherboard battery, dead power supply, dead video card, and dead monitor. It is likely something simple and cheap but could cost a bundle solving the problem when you can not identify the problem.
I didn't think it would be the motherboard battery because it should still get through the boot cycle (needing a resetting of the parameters). Power supply? It still gives too many other signals for it to be dead. It would possibly still have intermittent starts as possible. A dead monitor would not stop a reboot. I'd still say it's the motherboard.
So, it was motherboard. ASUS P4PE/RL was replaced including 1GB memory. The technician has explained that may be it was short circuit somewhere on the board or RAM bank. Some of you have made quite precise prediction. Thank you. But the story still has no happy end. There is some conflict with graphic card. The card is Radeon 9000 from ATI with digital and analogous output. With drivers and HydraVision SW it was possible to connect two displays and to arrange up to 10 desktops. Unfortunately, with graphic card drivers installed, Windows xp pro crashes with stop c0000415 and can be booted only in a safe mode, meaning that some drivers and components are not started. After de-installing graphic card drivers windows can be started in a usual way (with vga-driver?) but with messages that some drivers are missing and of course missing two display and multiple desktop functionality. Has somebody any ideas what is the reason for such behavior and in general what is a procedure to update windows after installing new HW ?
Hopefully this is not the computer you trade from. If so...stop stressing about it. Take it back to the computer repair shop...back to that technician... let them find the problem and fix it for you. When they do...such repairs come with some sort'uv warranty. That way if something goes wrong like 20 days from now...take it back again...free of charge and let them fix it. Computer problems is one of the last things that traders should be worrying about. Simply...if your not an expert at diagnosis (troubleshooting) and repairs...pay someone to repair it for you so you can concentrate on trading. Just my opinion. NihabaAshi
a5519: I have also had problems with ATI cards. For multi head cards dual or quad, I have had very good service from the Matrox G200 quad series and the Matrox Millennium G450 series.