|The SD card might be bad. Does it work in other computers or your phone/camera?|
The problem with the reader may be because XP is shutting off power to the USB port it's connected to. From:
"If you're experiencing mouse lockups or failures, it may be because your computer is automatically turning off the power to a USB Root Hub.
1) Go to your Control Panel > System > Hardware tab > and click on the "Device Manager" button.
2) In the Device Manager window, find the item or items labeled "Universal Serial Bus controllers." Open it, and double-click the first item called "USB Root Hub."
3) In the USB Root Hub Properties dialog, click on the "Power Management" tab.
4) "Allow the computer to turn off this device to save power" is checked by default. Uncheck this box, and click "OK."
That discusses a mouse not working but the fix would be the same for you if that is the reason.
Or it may be the reader itself. Mine does that too and I have the USB port shutdown option disabled
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