|The fan that you mentioned *may* be the CPU cooling fan. If not, it's probably the motherboard chipset cooling fan. Regardless, if it's there, it should work.|
Shutdown the system & disconnect the power. Open the case & try spinning the fan with your finger...does it spin freely? If not, it's either dirt encrusted or the bearing is starting to go. Clean the fan as best you can & give it a good blast with compressed air (blow out all the heatsinks while you're at it). Work the fan blade back & forth with you finger to see if you can free it up. If you get it to spin freely, try firing up the system & see what happens. If the fan still binds up, it will most likely have to be replaced. You *may* be able to buy yourself some time if you oil the bearing. Just remove the fan & carefully peel back the label on the underside to expose the bearing. Add a drop or two of oil & work it in by spinning the blade back & forth with your fingers, then seal it up & reinstall.
BTW, the term "CPU" refers to a chip that fits in a socket on the motherboard...it should not be used to refer to the PC case & all the hardware inside. Your CPU is a P4.