Video display damage to computers

I have seen a similar topic earlier but my question is little more suspect.

My monitor (connected with HDUSB15) suddenly went out of order. No picture except no signal. The computer with XP (computer A) did not boot and the keyboard did not indicate any LED function for CAPS LOCK. All leds at the keyboard were lit.

I took an older computer (computer B - fully working with it's own monitor) and connected it to the monitor. It worked for one day then I had the same problem. Monitor said 'No signal'. All behaved the same.

I tried a working monitor on A and B computers. Both were dead.

I also tried an other graphic card in both computers but no sign of boot.

I hear one beep but nothing more.

I checked the different voltages from the power supply and they are ok.

Can the monitor really damage the motherboard and in that case, in what way?