Most of the time, issues with wireless networked computers are with reception and interference and encryption.
Try the problem computer in the same room as the router -- not too close or other problems occur -- and see if things improve.
See if it can connect to the router's setup pages and once in there try disabling wireless security temporarily.
Alternatively connect computer and router by ethernet cable and disable wireless security, disconnect ethernet and try to connect by wireless .
I have 3 computers in my home accessing the internet off of Verizon FIOS's wireless router. My dell desktop has flawless connectivity. My wife's mac book has flawless connectivity. My Toshiba satellite shows continued connectivity but isn't really talking to the router. Efforts to ping the router result in sporadic replies. My laptop works fine in wi-fi hot spots, it works fine connected with a LAN cable to the router. I have checked all of my settings against the dell to ensure that everything is correct. I have tried Verizon's helpline to no avail. I have shut down my internal nic card and connected a Netgear USB nic device, exact same problem. Logging into the Verizon router show's me that it is able to see the laptop, but they don't pass traffic to each other; sometime it shows laptop status as active and sometimes inactive. I have tried shutting down my firewall to see if that was the problem...no luck. Is it possible that these problems are from an infection in my laptop? I have ran regcure to look for problems...no luck. I run avast anti-virus and online armor's free version for a firewall. I also have spybot running as well. Sorry for the lengthy post and thanks for any thoughts