If the computer still does not boot, there are a few things that can be done. First, check to make sure that all of the cables are properly plugged in and that the power supply is turned on. If everything appears to be plugged in correctly, try resetting the BIOS. This can be done by unplugging the power cord from the computer, opening up the case, and finding the CMOS battery. Once the battery is located, remove it for about 10 seconds and then reinsert it. This will reset the BIOS and may fix the problem. If resetting the BIOS does not work, try replacing the CMOS battery with a new one.
What to do if the computer still does not boot (can't see anything, black screen, etc)