I recently made a very stupid mistake. I was showing a friend something in my case and i bumped my cpu fan and broke off a blade. i replaced the fan but noticed that it doesn't speed up now. my computer will overheat and shut down it's so bad. I bought a much better heatsink and fan, the problem got better but the fan still won't speed up so under a large load it still heats up. I don't know what else to do to fix this. please some one help.

If we're dealing with a PWM (4 Wire) type system, generally you need to enter the computers BIOS and more or less tell it to track CPU temperature. Some aftermarket products are not compatible with Intel's P(ulse) W(idth) M(odulation) specs and may already be running at full speed. Or for that matter, their lowest speed. The motherboard manual should explain how to enter the BIOS, and which fan configuration settings are available.

my fan is only a 3 pin. sorry i wasn't very in depth on the first post. also my computer in a compaq and i don't think my bios is very useful, but i could be wrong.

Is the fan plugged into the motherboard or the power supply harness?

the fan is in the motherboard. one thing i thought was that i updated my bios awhile back, could that effect something?

Yes, the default settings could have been restored or altered during a BIOS update.

You could also test the fan itself with a 3 pin to 4 pin "Molex" adapter. (The same connector that powers the optical drives and what not. Many aftermarket fans come with these adapters. Running in that configuration though, some machines may not start, and some will blow up warnings about "CPU fan failure"

i had purchased a fan that ran on the "molex" adapter and it wouldn't speed up either. my fan seems to run at 1150 'ish rpm no matter what, and my cpu will get up to 40 c no problem.