Pendrive keeps on getting disconnected.

In my desktop all the pendrives keep on getting disconnected and then remount after a few seconds. I hav tried formatting with a different O.S (linux mint 9) but the problem persists. the pendrives work fine in other computers. strangely I connect to internet via USB port and it works just fine. my mobile mass storage devices also connect without a problem. I use xp with service pack 2.

it would be a great help if you tell me what is the problem.