No signal to monitor, no keyboard, no mouse issue.

A few days ago, my son accidentally put in a usb flash drive upside down in the front usb port to our HP desktop (it's a little over a year old so it's out of warranty). The computer went dead as soon as he did it. I unplugged everything then replugged everything back in and the computer powered on, fans worked, no beeps, but the monitor did not receive a signal and the keyboard and mouse did not work. I unplugged everything and left it alone for a few hours. Came back tried it again and everything worked fine. I was on the computer for a while and put it in sleep mode. I went to turn it on (take it out of sleep mode) and I don't have a signal to the monitor and the keyboard and mouse do not work again. I tired unplugging everything and replugging everything back in and letting it sit for a few hours, but that didn't work. The tower turns on, fans work, no beeps, but the monitor has no signal and the keyboard and mouse do not work. Any thoughts as to what the problem is? Bad motherboard? Bad power supply?