USB Drive keeps disconnecting

I have a very weird problem wiht my Vista Ultima x64. When I connect an USB flash drive to any USB port on the system it installs the drivers the first time i plug it in, the drive letter appears, the autoplay menu pops ups, and the it disconnects and connects again. If I use an MP3 player, it restarts, as if it were plugged off an on. I am using a C2D 8400 on an Asus P5N-e SLI bios version 1002, 4GB supertalent DDR2 800. It´s not a motherboard/chipset issue because the same thing happened with the exact same setup but an Asus P5KSE motherborad wich i swapped with the P5N-E SLI. It seems to happen with non-powered Drives, because I have an external USB hard drive with its own power supply that works, and my Nokia N91 cellphone works too. Any ideas?

Click Start, in the search bar type in: devmgmt.msc then press enter.
Have a look in your USB Root Hub properties/Power management and verify that the "Allow the computer........ is unticked.

I have also had the same problem. Except I am on Vista Home Premium 32bit. I bought a 200gb external hard drive to backup my documents and store all my music on because it took ridiculous amounts of space on my internal hard drive of my laptop. The external hard drive worked fine for ages, then it started randomly disconnecting itself of its own accord. Now its doing it every few seconds so I can't access my files. Google led me to this thread and I know all 3 of my USB ports work just fine because my printer, camera and phone have all worked on them. So I followed what Sid said, but it didn't make one iota of difference. It still disconnects and reconnects of its own accord. I've also scanned the drive for viruses and the like and it came back clear.

Does anyone have any ideas?

Regards,
Kim

Well, is it a 2.5 hdd tpe powered by the laptop or a 3.5 hdd type with its own power supply?
It looks like if the hdd does not have enough power to work.

It's a 3.5 hdd type with its own power supply

OK, then verify the power supply, for example exchange it to a similar one or try your hdd on another computer.

Ok cheers I'll try that

I've tried it on my home PC that runs on XP Home and it's fine. Connects and stays connected.

I guess it must be a Vista problem. Any more ideas?

Just a test, have a look if you do not have any probleme with the AC plug of the room where you use your machine, so just try to plug your hdd somewhere else.

Already tried and tested, doesn't make a difference. I went on the Microsoft support website and it said to download SP1 so I'll try that and see if it makes a difference. Other than that I'm at a complete loss.