My pc is acting strange what can i do/?

It started acting eird about a month ago,restarting ad stalling, then when i turned on it appeared to br running but the screen would be blank, i had to keep trning off and on about 5 times,until it came back ok, but sometimes it would freeze at the windows xp logo or make it to the normal screen and restart, had it formatted about 3 weeks ago, and it is actind the same, a message came up saying it could be a hardware or software problem but i have not installed any hardware or software it did not have before,also checked for virus and spyware and it is free,about 2 days ago a windows diagnostic message came up saying it was a memory or ram problem, buy i as said earlier i have not added or removed anything,my pc is just over a year old,hp pavillion desktop a1500la,512 ram celeron 3.2GHz, windows xp.I need help since i don't know anything about computers

My pc is acting strange what can i do/?noton

what diagnostic program? - CHeck for spyware and virues

good spyware utility Spybot Search and Destroy (be sure its by www.safer-networking.org the reset is likely spyware its self.

if its a legitimate diagnostic program trust it. if its not a spyware/virus problem its very likely hardware. without hardware to swap in and out to test it all you have to trust is the diagnostic. also, carefully re-seat the memory sticks and video card (if youve never been inside a computer then leave the CPU alone.)