[SOSAGES]

well u know what the problem is - if u havnt changed anything and its worked fine for 2 years then it seems somehow the router has screwed up.

try restoring to factory conditions and set it up again see if it happens - not sure how ur connecting exactly i assume both pc's with nic's pluged into the router - try swapping nic's, do both pc's lose connection ? when it happens can both pc's still ping each other? lots of stuff it could be - just go slowly and eliminate each thing that it could be nic / cables etc