A strange occurence.

Okay computer people. My computer recently stopped working off wireless. tho it recognizes the wireless network and says its connected, it cant access the web without an Ethernet cable. Ive had the computer since august of 2012 and its always worked perfectly fine, but since two days ago the computer will not and can not connect to the internet wirelessly, but will show that it has a stellar connection and says it working fine when i run diagnostics... Any think they could help? or know if i could take it to Apple to fixed? and if so how much? Im very concerned, thanks 😉

P.s i downloaded something from the app store and it says i have quite a bit of viruses but no infected files. Could this be due to a virus? even if nothing is infected?