It sounds like you've picked up some kind of malware that defeats normal virus protection. This is no reflection on McAfee as there are such entities out there. One just has to be very careful.
I'm hoping that you can do the following which will hopefully get you back to normal.
You have a choice of two methods.
As you don't state what your operating system and service pack is I'm assuming you have XP SP3, Vista SP2 or Windows 7 and are up to date with same as far as Microsoft Updates are concerned.
It's very important to keep everything, system, software etc. all up to date. Also always ensure the system clock is accurate, time and timezone-wise.
Try booting to Safe Mode by tapping F8 repeatedly while booting up and selecting the first item on the ensuing menu.
This boots your PC into a semi-active mode which usually prevents malware from running.
Once booted into that mode go to Start/All Programs/Accessories/System Tools/System Restore and endeavor to restore the machine to a date/time that you know when it was OK and then reboot and hopefully it will be restored.
Make sure to check for Windows Updates immediately afterwards and to right-click the McAfee taskbar icon and select "Check for Updates", otherwise it may malfunction.
Method 2 and might be a good idea to perform in any case.
Go to Safe Mode with Networking by tapping F8 repeatedly while booting up and selecting number 2 on the menu. This (hopefully) gives you internet access in Safe Mode.
Go to THIS site and download the FREE version and update it once installed and then run a full scan and let it remove anything it finds and reboot immediately when asked to.
Hopefully that will sort things out for you.
If it does help run that second tool again in regular mode for good measure. It's a good tool to keep for such emergencies but remember to keep it updated.
Many thanks for your assistance.
I have followed both your suggested methods.
Method 1 - It seems to have worked and I am monitoring the situation.
Method 2 - Actually I tried this method first and I seem to have got into a mess here.
I downloaded Spyware Doctor free Edition and it identified a number of
threats and infections, but said I'd have to buy a different version to
remove these threats etc. - It also recommended deleting McAfee first
but I didn't want to do that.
That's when I switched to method 1.
But now my McAfee won't work, nor does the Spyware Doctor
and even AVG can't be downloaded - as a conflicting program.
At the moment Windows Firewall and McAfee Firewall are ON
Windows Defender is also ON
McAfee Anti-Virus and Anti-Spyware is OFF and won't be switched on regardless.
I decided to uninstall Spyware Doctor but I can't find it on my computer.
So now I have a bit of a mess.
If you think there's a way to resolve this challenge I'd be really grateful for any help.
Maybe a private mail would be best - if the topic is not of
any interest to others.
I did say I'm not very good with computers - Sorry.
But thanks for your help.
Method 2 was Malwarebytes. The free version of that is far superior to Spyware Doctor in my opinion.
If you can't find SD on your machine I wouldn't worry too much, it's pretty useless anyway.
Perhaps the System Restore wiped it so I wouldn't worry about it.
If the situation stays OK I would turn off System Restore and then turn it on again. That will get rid of the infected restore point.
I would strongly recommend you use Malwarebytes free now to be sure and don't forget to update it before running.