Mac dying!!! needs YOUR attention!

hi all

ill get to the point, ive got a g3 powermac? clear case with perspex handles. I wanted it for my bf to use, he bought me a lovely new imac but i want to try and revive my old mac for him.
Basically, it will run for a few mins then it will cut out and you can't switch it back on for about half hour afterwards.
I'm pretty sure its a hard drive failure but would like some conformation. Also if it is the hard drive can i just replace it with a new HD? the model of the HD is a seagate barracuda, ive looked on ebay and they seem reasonably cheap, so would be willing to replace it if thats what the problem is.
i have completely wiped the disk and there is no os operating on it. I know everything is working as ive literally just tried to reinstall tiger and it switched itself off, so it must be a hardware problem.


Any help would be great,

thanks

franny
xxx

The hard drive is a common point of failure. You can run the Apple Hardware Test to check it. If you choose to replace it, bear in mind that you can use any PATA hard disk. You do not need to purchase the exact same make and model, just make sure that it uses a traditional IDE/Parallel ATA connector instead of the more modern SATA style.

Also note that many times when a machine shuts itself off and then will only turn on after a period of time, it's usually due to a thermal issue (like a bad fan). Have you confirmed that the fans are all functional?

Could be a power supply problem or an intermittant capacitor fault on the motherboard.

When ancient G3 iMacs start to die, there's usually little point trying to fix them.

all the fans are working, the insides were cleaned out recently (by someone who knows what they are doing!) there is no grinding noise like you get on a pc when the hard disk fails.
im not a computer hardware geek, so the 2nd post makes no sense! the light on the motherboard does light up when it is running.
im at a loss, i know its an ancient mac and i can prolly go on ebay and pick one up for £40 but would ultimately like to fix it. Before this started happening it was dead reliable.
it has had a new power lead recently, was one of the first things i replaced.

hmmmmmm??