Or you have 2 odd wifi parts (the old router and that laptop.)

When I see this I try the old second wifi router trick. It's about post 18 in this forum. Armed with router #2 plugged into an Ethernet port of the first router setup per this forum's stickies it usually cures the issue. It will not cure it for those that insist on one router or can't accept a dual wifi router solution.

Good luck,