Power to USB lost when computer is under load

Any time my computer uses 50+% of its CPU for more than a few minutes, the power to my USB ports seems to be shut off, and then the CPU spikes to 100% and stays there. (syncing my iPhone is what was causing the 50% load)

The only thing installed is MS Security Essentials (real time scanned is turned off), and iTunes. It is a fresh install of Win 7 from 3 days ago. I guess it could be a virus, but I doubt it considering the OS is fresh, and the PC hasn't been used much.

I have never seen anything like this happen before, and am at a loss as to what would cause it. I could just re-format again, but I would like to solve the problem. Anybody have any thoughts?

If it matters, the general specs are 2.7ghz dual core with 4gb ram.

edit: I didn't mean that suggest it was iTunes, I was just pointing out what was causing the load. I have seen it happen with the system under load and iTunes wasn't running. I'll try prime95 tonight and see what happens.

Also, let me point out again that the cpu is only under 50% load when this happens. the fact that it jumps to 100 is a symptom, no?

edit: I formatted the drive and started from scratch. Running prim95 has no effect on it. However, I installed iTunes and the symptoms appear. Maybe it is iTunes. Any other ideas? Let me also add that nothing is in the event log.

edit: As far as I can tell the PSU does not have enough power to charge the iphone, run the wireless adapter, and the CPU at full speed. I think power to the USB is being shut off so the rest of the system gets enough. (does that make sense?) If so, I would mark molly's point about the PSU being insufficient as the answer, however it is a comment. If you make it an answer I'll accept it. :)

user1808

Posted 2009-11-02T18:52:05.590

Reputation:

4what iTunes does to a windows installation is worse than most viruses ... they're easier to remove too. :) – None – 2009-11-02T18:58:36.793

Answers

I think your assumption that it's a power failure may be wrong. I would suspect a crash in the USB driver first. The symptoms look almost the same, and a crash is much more likely than such a selective power failure.

TheSmurf

Posted 2009-11-02T18:52:05.590

Reputation: 456

I pointed out power failure because devices like my mouse/keyboard still work. It is my wireless adapter and iPhone that lose power. Now that I say that I realize that the mouse/keyboard are using power so that is interesting. I wonder why the other two devices lose it..... – None – 2009-11-02T20:29:15.563

I take it your mouse and keyboard are plugged into your PS/2 ports? – Matthew Ruston – 2009-11-02T20:46:01.600

no, they are usb. I was saying it is odd they still get power, but other devices lose it – None – 2009-11-02T21:20:37.100

kbd/mouse probably aren't drawing much power; iPhone & wireless likely want bus max. power (500mA iirc). – quack quixote – 2009-11-03T05:05:49.053

Joe: It's entirely possible that your keyboard and mouse are on a different bus... – TheSmurf – 2009-11-05T18:30:10.673

You could try running Prime95 or SuperPI in order force CPU load and see if the problem persists. Using something other than IPhone Syncing to obtain high CPU utilization allows us to potentially exclude blame from iTunes.

As for actual soltuions, my first suggestion would be to see if there are any BIOS updates for your motherboard or updated USB drivers for your hardware.

Matthew Ruston

Posted 2009-11-02T18:52:05.590

Reputation: 1 149

+1 run a 'burn-in' test to determine whether the PSU is suffient or not. http://files.extremeoverclocking.com/file.php?f=213

– None – 2009-11-02T19:17:53.367

Given that it's happening during iPhone syncing, I'd tend to blame the sync process immediately, rather than a power failure. – TheSmurf – 2009-11-02T19:43:58.760

1no, i'm with Molly; make sure the system actually has enough power. CPU kicking into overdrive will draw more power; if the PSU isn't beefy enough, a power drop elsewhere in the system is possible. – quack quixote – 2009-11-03T04:05:51.373