Wireless nightmare

Hi all, perhaps someone can help me with a 'wireless' query..

I recently purchased a wireless router (BT Voyager 2091) for use with my PC, a desktop (Philips Freeline LS1200). Thr router seems to work OK and after some tooing and fro'ing it is picking up a wireless connection. The problem is that the wireless signal is pathetic and drops in and out, 30 seconds on 10 seconds off roughly, over and over again. Also, I'm only picking up the wireless connection when the machine is hard wired, when i remove the ethernet cable the wireless connection is lost!!!

The PC has a built in LAN card, which is a Ralink RT2500 (although from recent research this may not actually be the make, just the chipset???).

Would appreciate any help guys, I must confess, I am not the most 'technically gifted' when it comes to computer matters so really need help with this. BT have suggested, after they couldn't do anything about it, that the problem may lie in the LAN card???

 

I have installed a 2091, with two pci cards one in each of my desktops. I had to position the router so that both coputers could communicate with the router. which meant the router ended up in my lounge.I also bought extended arials that took the place of the arials on the pci cards. I now never have a problem with being dropped, losing connection. My ISP is BT.