|According to what you described the problem is showing with the motherboard itself . I'm not sure of the brand and model number than your currently using, however the normal method is to remove power completely from your computer. Then remove the CMOS battery from the motherboard inside your case.(This looks like a small round watch battery.) Leave both the powersupply disconnected and the battery removed for at least 3-5 minutes before putting it back in and plugging your computer back up.|
After this you will have to reset the time on in the Bios but there should be basic instructions provided based on the brand that you use.
If this does not work there is several factors that could play in the other issues.
The normal things that has issues related are the video card, processor(cpu), the memory(dram), and the motherboard itself.
However, there has been several cases of those that still use Dial-up service in areas that are not supported by cable or dsl providers that have issues with weather. Overvolt and Undervolt(power outs) are affected very commonly through the phone lines will shock the modem and cause your computer not to start.
To test if this has happened follow the previous steps of clearing the CMOS and additionally remove the dialup modem from your computer and check to see if it will start now.