The power fan and CPU fan is doing fine.

But the cooling fan which is used on the inside of the computer(mother board, harddrive...) isn't working

Is that mandatory? Since the fan comes with the case it's a bit hard for me to change it.

some computers don't need fans at all, but if your case came with a fan you probably need it. cases are designed with airflow in mind so if the fan breaks everything gets out of wack. without a case fan the heat from your cpu has nowhere to go; it just recirculates in the case this will cause problems. a case fan is cheap and very simple to put in (4 screws & 2 wires, I usually pull them out of old AT power supplies so they are free for me.) so if you think you know more about cooling your case then the guy who designed it go ahead and melt your cpu.

Grab an app to monitor the temperature. My case came with some gay case fans with lights that were hardwired in. I dealt for a while but it's in my room and now it's on all the time hosting stuff I took the fans out and haven't replaced them yet. My Athlon X2 used to idle at around 29C and without the fans it has jumped massively to around 39C but that is still plenty low enough that I'm not concerned.

Check the temps yourself and make educated decisions rather than asking questions when nobody (including yourself) knows enough to give an answer worth reading.

If you decide to just keep an eye on the temp be sure to find out what normal operating temps are for your specific cpu; they vary wildly! my p4 desktop will do an emergency thermal shutdown at 60C but my powerbook hit 78C last night and the fan hadn't even turned on yet. My point was I was able to rip a fan out of a power supply that had been sitting in my dad's basement for at least a decade and put it in my desktop just fine. I soldered mine in but even if the bad fan was hardwired in all you need is a knife and some electrical tape. it just takes 12v. the whole thing didn't cost anything and took like 20min. I've had a cpu melt for lack of cooling before, and that sucks a lot more then just putting a new fan in. even if you do you should keep an eye on the temp.

I would say depending on your ambient temp it is certainly needed. At least take one side cover off to let the heat escape until you can replace the fan.

KC

Fan is attached to the case so I dont' know any easy way to replace it.

CPU is at 47 degree. Should still be runnable.

For the other part I have no idea. Hope it won't burn.

ps. arh, I see 4 screws attached to the system fan... maybe it's not that hard to change...