Hello. I'm a new PC builder and only know the very basics. I just built a new computer and at ran into a few problems. My specs are: Case: Antec P180 (3 fans) MB: Asrock 4coredual-vsta CPU: Intel e4300 (1.8ghz) RAM: 2GB Kingston DDR2 667 VGA: NVIDIA 7600 GS (edit2) HD: 320GB Seagate IDE PSU: Thermaltake 430W I connected everything (don't know much about PSU, just connected them all, I'm a bit ignorant about the whole voltage thing) and at first it works fine. I let it load and do the disk format thing when installing XP and leave it on while I fell asleep. Few hours later the computer is off. I turn it on and it turns off a few seconds later with nothing on the screen. Tried turning it on around five times and the same thing happens. I leave it alone and look on the internet for some solutions and then tried again. The computer works fine for around 20 minutes and then shuts down again. I try again and then it shuts down few seconds later. I turn it on in the next hour and it lasts for 1-2 hours before shutting down again. I look online with people with similar problems and ones saying its the CPU, the other says its the PSU, motherboard or RAM. I don't know who to listen to. I downloaded Speedfan and Core Temp and ones telling me around 75C. I freak out, go to the BIOS and set the CPU clock speed down. Now its running at 1.20GHz and its still pretty high (speedfan:50C when idle 75C when load / coretemp: 67C when idle and 75C when load). I think its the CPU because when I installed it, I accidentally lifted the heatsink, maybe trapping air in the thermal grease. Also, the heatsink caps that lock onto the motherboard are not fully down because the other two won't go all the way down, even though its attached to the MB, just not securely. Can anyone please tell me if its the MB, CPU, or PSU? Kind of low on cash and can only afford to buy some thermal paste to reattach the heatsink. By the way, my computers running around 2 hours so far without shutting off completely. Edit: One more thing.. everyone keeps mentioning the computer making beeps when it boots up but mines makes no noise. The only thing that makes noise is the DVD drive and the fans. The computer works though.