OK, a few possibilities. Even if you are able to download Malwarebytes' onto the PC, it's quite possible that you won't be able to install it while the infection is present. I'd like you to visit this webpage for to familiarise yourself with ComboFix:
http://www.bleepingcomputer.com/combofix/how-to-use-combofix
NOTE: When you download ComboFix.exe, rename it like so:
In order to get it onto your system, is it possible for you to download it on another computer and burn it onto a CD? Alternatively, see if you can download it on the infected PC. Even without the mouse, it should be possible to download it using just the keyboard. Try pressing the
Windows key + R , typing in
iexplore and press Enter. This should bring up Internet Explorer. Use the tab key to go into the address bar and type in the address of one of the download locations:
http://download.bleepingcomputer.com/sUBs/ComboFix.exe
http://www.forospyware.com/sUBs/ComboFix.exe
http://subs.geekstogo.com/ComboFix.exe
Alternatively, try going into Safe Mode with Networking. When you are stuck at the black screen after logging in, press Ctrl + Alt + Del. Then press
Alt -> F -> N to bring up the Run dialog. Type
explorer.exe and press Enter. This should bring up the normal Desktop.
It may be extremely slow with 100% CPU usage, but hopefully it should eventually load. If you are able to run ComboFix, run it and post the log it generates. If not, please let me know what stage you were able to get up to.
If I copied everything to the external drive would this solve the problem?
Just copy the files that are to be kept then format and reinstall?
Yes, but I was under the impression you were unable to see the external drive at all when it was plugged in? Please clarify this point. If you are able to see it, try using the external drive to copy across ComboFix.