My fan goes Crazy when turning on PC and monitor light stays orange

Has the system ever worked (since you have had it)? What fan (case fan, CPU heatsink/fan, video card fan, power supply fan) are you referring to?

it's a heat sink fan
AUSTIN power supply max: 300 watts
. it doesn't do any beeping noises when i turn it on. but it turns on and powers HDD and DVD. Just the fan immediately starts going nuts and monitor stays oragne

Sounds like the board is failing to post.

Strip it back to the basics to reduce pull on psu, 1 piece of ram, no drives connected.

If that fails, pulll all the memory and see if you get an error beep, thats ok.

If so, put back in 1 stick of memory and pull graphics card unless onboard, if you get error beeps thats ok.

If you get this far, reseat heatsink and apply new thermal paste.

If no joy, motherboard is fubar.

As for 20 pin psu in 24-pin socket, if this is the original psu, don't worry, if not, could be not enough juice to motherboard.

I did everything as you instructed. no beeping noise whatsoever and i added thermal paste.I have an onboard graphics card. the psu however was added from one of my older comp's. it didnt come with a psu so it was just a sacrifice. maybe not enough juice? is that maybe why the fan goes nuts. the comp turns on perfectly. keyboard lights go on, dvd light goes on. just the fan and monitor thats weird.

the fan will go to full speed if not posting since the BIOS is not loading to slow it down. You have some kind of hardware issue. Sounds like a dead mainboard. Did you plug in ALL the power connectors to the mainboard??? Double check everything. Try another PSU if you can. Re-seat the CPU, youve already tried bare minimum config by the looks of it and 1 ram stick at a time. Maybe dead motherboard.

Sounds like a 20 pin PSU connector into a 24 pin slot. Sounds like the wrong PSU for the job.

thnx alot for the replies guys. i'm gonna have to buy a 24 pin psu, maybe that could be the problem

the extra 4 pins are for the PCIe cards, they will not make a difference if the slots are unoccupied.

300 W should be enough to boot any machine of this type to at least the BIOS. Now, it might be that the power supply is bad, but in no way is is underpowered for this machine. In fact, many OEM's ship with 20 pin PSU's even to this day.