THREAT DETECTED, but antivirus is not helping. Why?

I am getting popup window message saying THREAT DETECTED(Trojan and others) repeatedly. I have installed two antivirus softwares McAfee and AVG, McAfee is 42 months old, but it has been updated through Internet. AVG is new. When I scanned throuhg these two softwares no virus was found . When tried to heal I got a message "This file can't be accssed"

THREAT DETECTED, but antivirus is not helping. Why?virus protection

Virus Detection and Removal:

Most antivirus programs can not scan, repair or remove file that are in use. So a normal scan of your computer while the operating system is running can miss many virus files.

Therefore it is necessary to scan your computer with a virus scanning tool that is able to do a boot scan. This basically means that it scans the HDD(s) for viruses before loading the operating system.

Another common problem seen is the use of several virus scanning programs at the same time. Find one program and use it and remove any others (that does not include ad-ware or spy-ware programs). Keep it updated; however most programs do this automatically if you have internet connection.

Deleting, repairing or quarantining files? Most programs offer this option when it detects an infected file. The best choice 9 times out of 10 is quarantine it. If the file is in your windows system folder a repair might be in order, but that is only if it is a required system file that has been changed, not a file added. Also repair operation rarely work. A good idea is to look at the log after the scan and see if any important files have been quarantined. You can usually just use Google the file name to find out what it is and does. If by chance a system file is beyond repair, you may have to do a system repair install to fix this.