Do you know the make of the wireless card in your computer? If you open control panel, then device manager a list will appear. scrollthrough this until you see the entry for network adaptors.
highlight the wireless card and right click on it. Choose properties, from there you can identify the card and we may be able to find some better drivers for you.
Also what OS are you using? Win 7 Vista etc.
Remember that if the computer has obstructions between it and the router, even though they are in close proximity to each other, you can still lose signal.
Can you also provide make and model of the router?