Reboot loop :(

Hello Guys and girls ,
So i have this problem on my pc ( Pentium 4 , 1536 mb of ram , 80 Gb hard disk , intel 82915g/gv/910gl Express chipset ) with windows xp sp3 ( i know it's old ) , i'm writing this so fast because it can't reboot anytime now :( I opened the pc and cleaned it , removed ram and put it back , Cleaned the power supply thing , Cleaned all the pc fans .. but when i turn it on , it lasts for like 10 mins and reboots and it goes to infinite rebooting after that , any suggestions or help please :( ? is it a power supply problem ? should i buy a new one ? any help please ? And i hear a sound ( like shhhhhhh ) before the reboot :/