Why is my USB inaccessible?

My 8GB Memorex Traveldrive thumbdrive works fine on my home WinXP Pro SP2 machine but when I plug it into my WinXP Pro SP2 machine at work it doesn’t show up in My Computer for 10-15 minutes though the thumbdrive light comes on. When it finally becomes visible, it apppears empty but when I get it home, all files are present. The intent behind the purchase was, of course, having a convenient way to carry files back and forth. Anyone have an idea what the problem might be and possible solution(s)?