please help

hi i have just installed a wireless router i have a laptop downstairs and 2 pcs upstairs the problem is i keep losing internet it says that i have an excellent signal and i am connected but keep losing my internet cant browse any pages or sign into msn or yahoo i can be on for a bit and according to icons in tool bar i am still connected with an excellent signal but when i try to browse internet it says i am not connected can someone please help me with this its driving me crazy even isp cant seem to figure it out im at a total loss never had these problems with wire router:4-dontkno