I have a custom built PC with an MSI X38 Platinum MB. It has worked great for the past 4 years up until recently. Lately my USB ports shut off randomly while I'm using my PC. My lighted keyboard and mouse suddenly go dark and quit responding. I can be steaming video from my PC to my PS3 and that shuts down as well. I can leave my PC IDLE and it'll work a few hours later, other times I go to grab a beer or something and when I come back the keyboard/mouse don't work. I'm forced to do a hard boot because none of the peripherals work to shutdown properly. It also happens while I'm typing or surfing the WEB. It has to be a MB issue, but I don't see how this PROBLEM can suddenly appear after years of normal use. I searched MSI's website for BIOS updates but they never work. There is one available but I use their online BIOS flash utility and I get an error and have to restore a previous BIOS version. I'm not even sure the updated BIOS is needed because it seems to be a simple upgrade for larger HDDs. I'm stumped and I'm about ready to buy a new MB just to solve this issue. I don't think it has anything to do with Windows. I'm using XP and did a fresh install on a new HDD because my old drive was getting too old for comfort. The problem still exists so I don't think it's some sort software CONFLICT. Control Panel/System/Device Manager/USB Hubs/Power Management...turn off Let Windows Turn This Off to Save Power...
Do this for all Hubs...
Stupidly enough this is the default Windows setting...I've done that in the past and the problem still exists. I will double check to make sure I didn't miss any, though.

*EDIT*
All of the hubs have that option turned off, I appreciate the IDEA, though. I've Googled a few times and can't find anything related to this problem. Maybe my MB is bad and has to be replaced. Make sure that you aren't using any of the sleep or hibernate functions. They can be very problematic on a desktop.I have all the standby/hibernate settings turned off, except for my monitor.