No video or USB signals from desktop

looking at my brother's PC - an HP s3000 slimline that went dead on him earlier this year. The machine lights up when plugged in, but there is no signal going to the monitor and I noticed that the keyboard lights also don't light up when connected. It's one of those PC's where the video plug is on the motherboard.

I pulled the HDD and stuck it into my PC and booted up to see what would happen. It did end up with a software failure message and suggested a recovery to factory settings since they never did any system restores. BTW, I was able to connect it first as an external HDD and retrieved all their photos and stuff. It went thru the recovery procedure successfully and obviously wouldn't boot up in my machine due to the hardware differences, so I reassembled it all back into the HP and gave it a go. No luck. The box lights up as usual, but the monitor says no RGB signal and no keyboard lights.

The plan is to just use the HDD as an external HDD for his new laptop, but I thought I'd ask around here if there are some tests that I can do before I scrap the machine. I looked online and on ebay for replacement motherboards and they are still over $240.

Can anyone think of why the USB and video ports aren't sending out signals?
I figured that the whole back panel with all the slots may have just shorted out.