IBM Thinkpad won’t enter sleep mode

After installing a CNET network card, my boss’s Thinkpad (w/ Win 98) won’t enter sleep mode even manually. Removed the card and still no sleep mode. When you close the lid, you get a ‘beep’ error. On shut down there is no more stand by option. AnIBM dealer told me to send it to the service center for about a week, but my boss can’t spare the time. Any help would be greatly appreciated.