Siemens SpeedStream 2604 Router linking issue

Question

when i connect my desktop to the Siemens SpeedStream 2604 Router the link light does not come on and my computer shows my network as being disconnected. when i connect it straight to the dsl modem it works just fine. so i tried plugging my lap top into the Siemens SpeedStream 2604 Router and it works on all 4 ports. i have tried restarting everythng and i still cant get teh desktop to link with the router. i have used this router on my desktop before with no problems, any help would be helpfull, thanks in advance