Why does the iMac G5 not power up?

My mothers imac g5 doesn't power up. No reaction at all. A few days ago it seemed to work perfectly fine.

A few weeks ago I upgraded the ram to maximum and upgraded to OS 10.5.8.

I did this because :

a) it had some Kernel issues

b) my mother bought an iPad and in order to sync it with the iMac it was nessessary.

But no luck, the usb connectors did not recocnize the ipad.

Otherwise it seemed to work perfectly.

But now it simply doesn't power up anymore.

No life signs at all !!!