I realize that this an old thread but..
Your CPU and/or case fans should normally spin up at full speed and slow down after POST. If they stay at full speed all the time:
The CPU is over heating - clean the thermal paste off the CPU and heat-sink. Re-seat the CPU and apply new thermal paste before putting the heat-sink/fan back on.
The PSU is bad. Find someone that can test it for you and verify that.
The worst case scenario. The motherboard and/or CPU is fried and need to be swapped out with new ones.
Another possibility is that the motherboard is grounding out on the case somewhere but this uncommon unless the computer was built by a novice.
One last possibility is that your graphics card is so shot that its causing your system to overheat. This would cause graphical issues during POST. (Weird colored blocks on the screen before windows boots up)-reply by DullBoy