power light not turning green just amber.not a power flactuation problem

There are a few things you will have to do. First, remove any newly installed card in the PCI socket if any. Try to re-sit the memory chip modules, that's removing and re-installing them. If they are two, try replacing one after another. Thirdly, try another VGA card incase you using the onboard one. Finally, swap your monitor. It must work. Good luck

please connect another power supply. it may be the course.

first thing I would check would be the power supply, then considering it's a dell gx260 I wuld check the capacitors (little cans shaped things) by where the cpu connects as some of these dells are notorious for having faulty capacitors. you can tell buy looking at them, they swell on the top mostly and some on the sides , then electrolitic fluid starts leaking out the tops. If you find these "leaky, swollen" capacitors, the motherboard will have to be replaced.
But try replacing the power supply first, it can be replaced inexpesively.
Regards..