random restarts

specs
athlon 64 3200+ 2.0
ati radeon x850 xt saphfire version
2 gigs of coraisr xms ram
550 watt power suplly antec
a8n-E motherbaord
i got rid of my firewall

my computer randomly restarts and im wondering what i should do to stop this.
i heard it was from windows frpom an emachine installed on a different mothrebaord. plz help

 

i heard it was from windows frpom an emachine installed on a different mothrebaord. plz help

I had trouble understanding that last part, but e-machiens ar eknown for having cheap crappy mobos, are there any emssages in your error log? and does the mobo make any strange beeps when it restarts? and you shouldn't get rid of your firewall, I would suggest downloading Zone alarm right away
http://www.majorgeeks.com/download.php?det=744

 

Has the machine always done this or is it something recent?

Does the machine actually complete the boot sequence and the just restart when it feels like it or does it continualy cycle thru trying to boot without ever finishing?

I also don't understand that last sentence.