Falkryn - thank you for the Trojan Remover link. I have downloaded it, run the scan and done the trojan removing bit. Hurray, I thought, until I restarted the PC.................low and behold there was the alert again!!!
So, I did another scan within the Trojan Remover programme and this time it said No malicious files etc. found

but the alert is still there. THIS WILL NOT BEAT ME!!!!!!
Nat - Thank you for your reply too. I will try anything, so will have a look at your suggestion.
Jan