Hi Brad, thanks for the tip, I had resolved it by the time I got your message as follows;
Firstly, as I could not access the site, I have my own webserver with full admin access so looked at the database and removed all the plugins then went back to the website and could see the screen again and was able to login...!!!
As it clearly related to a plugin, tested each of them and found it was the latest release of wpstorecart that caused it, installed the previous version and hey presto, all working again. I have sent a message over to the designers of wpstorecart with all the information of what versions of php, mySQL, OS, and plugins to see if they can find the cause and resolve it.
Didn't know about the debug feature, thank you I have now turned it on...
Demon