I am sorry for this issue.
We have to consider the possibility the board could be already damaged. However, you may try the following if this is an Intel® motherboard:
- Remove all drives, devices and internal cables connected to the board and the power supply also.
- Remove the CMOS battery for 20-30 minutes.
- Reconnect power supply only, RAM will not be needed (only the processor).
- Expect three beeps and the green standby LED on when you turn the system on. Of course you may want to check your motherboard has a piezoelectric speaker.
If you do not get beeps or LED from the board then it is damaged. If you do get them, continue adding the RAM in order to test for video.
In case further assistance is needed please provide the motherboard model number.