cannot connect to network when secured

I have a ThinkPad running Win7 Evaluation Build 7100 and all of a sudden I cannot connect to my wireless network when security is enabled. If I set the wireless security on the Linksys Router WRT310N to Disabled I connect right away. It was working fine with security enabled but it just dropped the signal last night and now it won't connect. The computer is now sitting beside the router and cannot connect when the security is enabled.

I have attempted WPA Personal and WPA2 Personal. The settings in the notebook are correct including the access key.

I thought it might be the router so I updated firmware - no joy

I tried another router WRT160N - same problem.

I can't think of anything else to try, any thoughts out there?

Thanks

 

Thanks Tony but I have changed it and the pass phrase a number of times