I just recently discovered that power was being fed back into my computer through an HDMI switch I was using to switch between my Xbox 360 and computer on my computer monitor. I discovered this by noticing my computer's case fans were running even though the computer was powered off. Even when I cut the power to my PSU the case fans continued to run. On a hunch I thought it might have been my 360. (Not too long ago I was playing Garry's Mod on my PC and was moving my 360 to another location. When I plugged the HDMI cable into my 360 (I had not plugged the power or ethernet cable in at the time) my computer screen went blank, only sound was still being transmitted via the HDMI cable from my computer's GPU.) Sure enough, when I turned my 360 off, the case fans stopped running. I have since unhooked the HDMI switch and no longer have the issue. So far my computer is running just fine with no issues at all. My question is, is there any sort of hidden damage I should be looking for, or is there nothing to worry about?