My Avast has been attaked and disabled

Viruses and worms
1

I have got something on my computer from a porn site that has now taken over my desktop and then puts up on the screen that I must pay with a credit card to get rid of this problem, Then restarts my computer if I do nothing. When I start Avast it says that it is not running and when I click on the fix problem button nothing happens. I tried to do a search but it won’t let me turn on the search for PUPs. I started in safe mode and avast looks the same. It let me do a scan but it found nothing. I tried to do a boot scan but I get a message that Avast can not do a boot scan on a 64 bit system. I deleted Avast in safe mode and reinstalled it from a jump drive but it says that Avast is still blocked. I took the hard drive out and ran a boot scan on that drive on another computer that had an up to date and working version of Avast, but it also found nothing. I don’t know what to do now. Does anybody have any experience with this sort of virus or with one that disables Avast. I have had another virus once that also disabled Avast and wouldn’t let me install a working copy in safe mode so I formatted the hard drive. Can a virus possibly be in the Ram memory and not on the hard drive? Any help will be very appreciated. Thanks, Joe

2
I tried to do a boot scan but I get a message that Avast can not do a boot scan on a 64 bit system
you need V5.1 or later to do 64bit bootscan

Try this

Malwarebytes Anti-Malware 1.50.1 http://filehippo.com/download_malwarebytes_anti_malware/
always update so you have latest database before you scan
click the remove selected button to quarantine anything found

post the scan log here

3

AMD Phenom™ II X6 processor 1090T
O.S. genuine Windows® 7 Professional
System Board… MSI 790X-G45
System Memory… 4GB composed of 2- 2048MB DDR3/1333 DIMMS
Hard Drive… 1TB 7200 RPM
Video… Radeon HD5750 PCI Express

Thanks for your response these are my system specs. I will download the antimaleware and run it but I don’t have the time right now. I will get back to you. I am running Avast version 5.1 and it gave me that message about not allowing me to do a boot scan with a 64 bit system.