What stands out (the most) in your post is, "ran registry cleaners galore". We find registry cleaners tend to create more problems, than they solve. With hopes the registry cleaners "did no harm", try the below.
Using Internet Explorer, download the below tools. If you're prevented from doing so, you will need to use another computer and transfer them to yours. (Using a CD/DVD or Flash Drive)
Download and run the "Rkill" tool. You will only need to launch one of files, in order for Rkill to work. (Right-click and "Run as Administrator") If you have no success running Rkill.exe, try the next. When Rkill runs you will see a command prompt window similar to this. When one DOES work (immediately) run a Scan with Malwarebytes' Anti-Malware. (See below) Do NOT reboot after running Rkill.
Rkill's purpose is to terminate offending / malicious processes. A more detailed explanation of what Rkill "does and doesn't do", can be found at the bottom of the Rkill download page.
You're also going to scan with Malwarebytes' Anti-Malware. The direct links for the installer and manual updater are listed below. To avoid any problems, rename the installer, prior to transferring it to your computer. Change it from mbam-setup.exe to kevin.exe. Don't forget to update, after the transfer.
Manual Update link
I would also recommend scanning with SUPERAntiSpyware. SUPERAntiSpyware FREE Edition can be downloaded from here.
If you run into any problems along the way, please post back and let us know ..
Don't know if this is all related but I got a few emails from friends that they hadn't sent (had dodgy attachments, I opened one by total mistake) found I had "Mirar" on my pc. Opera started crashing constantly. Tried removing Mirar manually, tried to uninstall it with no luck. Ran scans, registry cleaners galore. Then found I could not enable Windows Defender either.I uninstalled Opera and reinstalled (still crashes) I even tried Chrome which also crashed. Windows IE does not crash by the way. I use Vista. I have done all updates for everything. Any ideas ??