hey. the problem is that SOMETIMES the computer (whenever it is in windows OR even hardly reaches BIOS) restarts and goes into cycles of turning on and loading to the same point (sometimes not even managing to load POST) and off. Sometimes it works fine for a couple of days and then all of the sudden it gets in into this weird cycle. The way to get it out of this cycle is to turn it off completely, remove some components and/or shake it, altough even this doesnt help sometimes.
I removed all hard disks, CD and DVD -ROM, floppy, sound cards and was left just with motherboard, powersupply, graphics card and RAM and the same thing happened (totally randomly; sometimes it loads and works and sometimes not even gets to BIOS). I replaced RAM, graphics card, checked CPU with diagnostic software and did not find a mistake in those components.

Has anyone met with a similar case? is it the motherboard which HAS TO be change or the connections are wrong or maybe it is something else? please help - it is flustrating to have such a PC!
-thank you in advance!

You are caught in a boot loop, or whatever they call it these days. If you cannot even make it to BIOS it could be a power supply problem. If your power supply is good (and set on 250v), remove the CMOS battery, wait a few minutes, and replace it. If any of your CMOS settings have been corrupted this will reset them.

nope, it didnt help. still the same problem.... im so maaaaaaaaaad! :(((((( (n sad)

Does this happen on a cold boot or after you have been running I ask becuse it maybe heat related. Check and make sure you have the CPU fan running, if so you may try putting on some new thermo coupond on the processor heat sink.

well.. i dont believe it is heat related because well... when it happens after the pc is running for some time, i turn off the pc and when i turn it after some time, the same problem happens... but thanx for an idea.
you know anyway it is funny that i gave in this computer for fixing two times and they still didnt manage to find the problem....