Computer won't let me update windows

Noticed that computer has not updated windows for sometime. When I try to update it says system administrator won't let me but I am an administrator. I ran a Microsoft security scan and an antimalware scan and got rid of loads of viruses. I then restarted and tried again but same message comes up. Windows updates is turned off and will not let me turn on.

Windoze XP, 7, 8, Vista??

Windows 7. I managed to sort it out by deleting something under hll key or some such thing. However the computer is obviously infected. I ran anti malware three times and each time got rid of over 700 items. An annoying ad for comparing things keeps popping up.

Try to install Avast (free anti virus scanner) and run a boot time scan.
See the scanner settings to maximum \ most thorough \ slowest, will take a few hours to run but I find sometimes it picks up malware etc other scanners miss as they are running when PC is processing.

Install Malwarebytes (free) and run a scan.

Thanks for the relies. Have already run malwarebytes 3 times. Each time it list over 700 threats which I delete. So it is not catching the root. Currently doing est online scan which is taking hours and has come up with threatsalresdy. If that doesn't work will try avast.

Its a bit crude, but you can download and run Combofix from here http://www.bleepingcomputer.com/download/combofix/.

It will take about an hour to run, and reboot after. It will give you a log that wont tell you very much, but it does delete anything that it finds as being dodgy.

As with any of these tools, backup your important files before you use it. Ive used it many times without any issue - but I'm sure it has the ability of going wrong!

As a last resort - reformat and give your machine a fresh start.

After backing up your documents etc. of course.

Thanks scans now clear and also did an adware one. Getting error message on start up about bubbemage.dll not there - don't know what that is but it doesn't affect anything. Also there is no tray icon to update to windows 10 yet. Not sure if that is because it has only been updated after a few months.

Don't ever be without the FREE version of CCleaner :- http://www.piriform.com/ccleaner

Buy the Pro version if it's good enough