Are you using wireless B or G? G is faster but B has a beter range. Might be worth checking what your using, you may be able to switch to B if speed isnt an issue, B is still fast but just not as quick as G. The signal is also affected by things that get in its way. A friend of mine bought all the wireless gear to set up a network a while back and couldnt get any signal at all just down their house being realy old and having very thick walls and lots of wiring in the way of the signal. You may be able to get a booser or high gain areal which will improve the signal.
What kind of wireless card you using in your PC? If its USB and just pluged into the back of the PC you could allways get a USB hub and place it somewhere a bit more strategic so theres less interference between that PC and the router.