Replaced card reader------same problem

A couple of weeks ago I installed a USB PCI card with a 9-pin internal header which connects to an internal card reader that I, also, recently installed.

At times, I can insert a SanDisk or a MMC card and things are fine----green light stays on (card reader) and it reads the cards OK.

Other times, I can insert either card---the green light goes out, it does not read the card, the various slots (drives) do not show up in My Computer; but, the front USB port on the card reader continues to work OK.

If I restart the puter----the card reader slots remain "out"; but, if I completely shut the puter down---wait a few minutes and boot back up, the card reader slots/drives are functional again.

Update:

I returned the card reader to Newegg and received a replacement (same model as original); but, the same problem exists.  Any suggestions?

Dimension 8400
3 GB SDRAM
3.4GHz
160GB
Samsung CD-R/RW
Philips DVD+RW
Iomega HDD 80GB USB 2.0
Radeon X300
WinXP w/Service Pack 2
USR 8001 router
DSL
Firefox browser