My slow internet

[D.M.]

We have 2 computers at home, only 1 of which isn't working correctly.  About 2 months ago we got a cable modem (through Service Electric) and a Network Everywhere router.   I had both computers running through the router, but one loaded about 20x faster than the other.  The obvious problem seemed like the router.  My next move was to connect the slow computer directly to the modem using the  USB.  The slow computer says its connection speed is 12Mbps, while the one running faster is only 8 Mbps.  
Any ideas on the problem?
Thanks.

[merlin_2]

what nic cards <realtek>what o/s and what config have you used mshome 192.etc...is the slower one defraged clean internet history disk clean up....

[D.M.]

It had been defragged, etc.  Messed around with the anti-virus software last night.  After hours of uninstalling, installing, and tweaking it finally works as it should.  Thanks for the suggestions.