If not even the boot up screen is showing and you found it's not the RAM, it's either a video card or a motherboard issue. If you replace both, the problem should be solved. But, of course, because of price and compatibility and such, only replacing the video card is a viable option, and if it's the motherboard replacing the whole PC is the thing to do.
I changed my OS from Windows XP to XUBUNTU. It was working fine for the first 2 days. Later it the following problem occurred.
The system is running(LED is glowing, CPU fan is running) but its unable to boot up. Not even the boot up screen is showing up. What could be the issue? I tried removing my RAM and running the PC, even then no response. I placed the RAM into the other slot and tried running the PC, even then no response.