After firmware update 3rd comp getting really slow connection speeds. really slow.

I have a Dlink dir 625 and I updated the firmware because my browsers on my new hp 1030us would hang after about 5 minutes of use. After the update my 2 comps connections work great, but now my roomies comp is super slow to almost not there. Besides the firmware update I changed from wep to wpa/tkip encryption. I tried up dating his drive but its already up to date and before the update on the router his internet was really fast. His adapter is a wmp300n by linksys.

Please help as I think his head may implode with out the speed as it was before and I dont want to have to explain said implosion to his pops.