Do you hear a beep when you reconnect the power cable?? Pay attention because if you do CMOS is telling what is wrong with your pc Computer Post Beep codes
1 Beep (No video) Memory refresh failure Bad memory
2 Beeps Memory parity error Bad memory
3 Beeps Base 64K mem failure Bad memory
4 Beeps Timer not operational Bad motherboard
5 Beeps Processor error Bad processor
6 Beeps 8042 Gate A20 failure Bad CPU or Motherboard
7 Beeps Processor exception Bad processor
8 Beeps Video memory error Bad video card or memory
9 Beeps ROM checksum error Bad BIOS
10 Beeps CMOS checksum error Bad motherboard
11 Beeps Cache memory bad Bad CPU or motherboard
If you don't hear a beep. Don't be afraid and open the case. Check if the fan for the CPU is sppining and check if there is a wire from the power supply to the motherboard. MAke sure that the video card is connected correctly. Maybe the computer is booting up but you don't see it. Hope it works