The PUM.Disabled.SecurityCenter bit is not a real problem - PUM stands for Potentially Unwanted Modification. Some antivirus programs turn off Security Centre notifications so that you don't get two messages when your preferred one is disabled or turned off (one from your preferred antivirus software and then another one from Security Centre itself).
Some nasties manage to hide themselves in a way that will let your antivirus or malware software find something, and delete what they find, but reinfect the machine on a reboot - no I don't know how it's done, but I had one like that a couple of years ago which also stopped me from getting access to a lot of the major security software websites and prevented me from accessing Task Manager even in the Admin user in safe mode.
So a few things to try. If you can get to the site in safe mode with networking, try the free Sophos scanner first
http://www.sophos.com/en-us/products/free-tools/virus-removal-tool.aspx is the download site.
If that doesn't work, on a clean computer, download one or both of Kaspersky Rescue Disk (the link is
http://support.kaspersky.com/viruses/rescuedisk ) or the Avira Rescue Disk (download site is
http://www.avira.com/en/download/product/avira-antivir-rescue-system/product/avira-antivir-rescue-system/product/avira-antivir-rescue-system get the ISO rather than the exe), burn to a CD, then boot the infected computer from the CD and run a scan.
I haven't used the Kaspersky one, but if it needs to download updates before it scans the computer, let it do so. The Avira one is updated regularly, sometimes daily, and doesn't need to download any updates. If you really want to do a belt-and-braces job, do a scan with both of them, though that might be overkill.
If, after getting things cleaned up, you find that you can't access Task Manager, there is a program called RRT which will let you reset the permissions to that and a number of other things. The demo version is free (it has some restrictions, but should still let you reset the things you need to reset, or did when I last used it) and it will probably come up with some advertising to try and persuade you to buy the full version. The download site is
http://www.sergiwa.com/modules/mydownloads/singlefile.php?cid=2&lid=1
If that lot doesn't work, I'm out of ideas for home brew fixing !