external usb drive problem

Hello everybody. New member here at the forums.

I am having a problem with an external USB drive. I recently bought a Western Digital SE16 7200 RPM 320gig SATA hard drive. I purchased a CompUSA enclosure (for lack of finding any other brand in 5 different stores I visited) for the drive and a PCMCIA card that has USB 2.0 slots (my laptop doesn't have any). My problem is that I can only access my drive for about 5 to 10 minutes before my computer locks up. The LED light that tells me that my external drive is being access stays red constantly. The only remedy to this is to unplug the USB cable, then my computer starts working again. I have to restart my computer and restart the drive and try again only to get locked up again 10 minute later. Can anybody give me any ideas on where my problem is (the drive, case, PCMCIA card, or even the laptop)? Thanks; any help is appreciated.