I appreciate all of your help with this, but I think we've exhasuted all avenues...I bought a new wifi card today for £1.20 and it works first time.Cheers for all of your help anyway Rick! 
Dell Inspiron 1545 used to connect fine to Wireless - now doesn't.It can detect the avialable wireless link, but not connect to it.NOTHING has been changed prior top this happening.The router itself is fine and other devices connect to it no problem.The laptop connects with the ethernet cable plugged in fine.I have tried the following to correct issue:* Full Windows 7 re-install / Full Windows Update* Re-install drivers from dell site.* Reset router to factory settings* IP Config renew / flush dns etc..etc...* Laptop does not connect to other wifi* Uninstalled antivirus / firewall etc...Could it be a hardware fault????Would really appriciate help - wasted about 4 hours on this.
Inspiron sees wifi connection, but wont connect - tried EVERYTHING