personally its probally your router, how long have you had it and which one is it, mines stays on 24 hours a day, and over the years it haves it affects.
I had the same problem but mine was permantly off, rang virgin and there connected a laptop directly to the router via ethernet and it worked fine.
maybe worth a try, this would defo rule out the router and virgin if it works fine via ethernet.
other then that, buy a new router from pc world, currys or comet or even argos, try it if it still odes not work, just return it nothing loss, if it does then its sorted.