a threat has been detected on my pc what should i do ?

Where does the threat come up? Is this from your own anti-virus, which you have installed?

If not, it is very likely to be a malware itself, and clicking on any part of the message will download the malware to your computer (A fairly standard Trojan attack method - trick the user into thinking your malware is actually an anti-malware)

My first instinct is to immediately navigate to a site like google, which you know is safe. My second would be, if you haven't already, to install a reliable antivirus and run a scan of your computer.

Not sure what account you are talking about but standard procedure is to change your password ASAP. Also run a virus and malware scan if it is that kind of a threat.

Free virus/malware removal software on my website at- http://crazyfreesoftware.com/Security.html

Install an antivirus program