You maybe having something interfering.
Things I've seen cause interference near the computer.
Cordless keyboard and mouse.
Corded USB headset.

Other devices that operate on the same frequency as your router. (2.4Ghz)
Cordless phone
Microwave oven
2 way radio (walkie talkie)
Dish network receiver/remote

Settings you can try in your router.
Change the channel
If you have all G devices, set router to G only, not mixed or B+G
Check the QOS, make sure something else isn't given priority for bandwidth

Also if it has to pass through a wall or floor, try moving the router, the straightest (not angled through walls, floor) path and avoid heat and cold air return ducting.