System wont start..

[patkim]

I have an old PC that is based on MSI K8VMM Socket 754 board, Sempron processor, 512 M RAM stick and 400 W Powersupply.

Now the system won't start. When I press Poweron, the Power LED glows & CPU fan runs just for a fraction of second and it stops immediately. I can make out that even the PSU Fan is not running.

I am testing with only above basic components. HDD & other devices are disconnected for now.
The same PSU works well with another PC that I have.
Could it be that motherboard has become faulty now?
What makes the power supply cutoff immediately upon powerup that is as good as not powering up.
Thx.

[Steve R Jones]

What's the history behind the pc? Has it been stored away for a long time and you just now got it out? Or has it been running fine until today?

Dead cmos battery is a possibility.

[patkim]

PC has been in use occasionally, say once or twice a week.

[Train]

How dirty is the case?
Look under the cpu fan, is it plugged up?

Sounds like the cpu is overheating.

I use canned air that I buy to remove the dust and junk and something like q-tips and 90%+ alcohol to clean the fan blades.

[Ol'Tunzafun]

Check the motherboard for leaky or bulging capacitors.

http://www.pcstats.com/articleview.cfm?articleID=195
http://home.earthlink.net/~doniteli/index27.htm

[patkim]

Have done some clean up of CPU fan and overall dusting of mobo. At least the dust has been removed now to a good extent.
However system still refuses to start :-(

As I am trying out, one new observation, if I unplug the CPU power i.e. the 4 pin connector, and then hit poweron button, the PSU fan runs and the Power LED keeps glowing!!Of course CPU won't operate now but at least the PSU runs!

Thanks for the links too, will try to inspect the mobo for any bad capacitors.