Hi Pepy,
You might try running scannow on the system and see if it can piece itself back into order.
sfc-scannow
Scan and repair the system. The sfc /scannow command will do that - it will scan the operating system, looking for corrupted files and inconsistencies; it will replace and repair whatever it can. If it finds corrupted programs or libraries, it will try to fix them.
- Start Menu> All Programs> Accessories> Right-Click Command Prompt> Select 'Run as Administrator'
- In the Command Prompt Window, type (or copy / paste) sfc /scannow and press Enter.
(Note the space between sfc and the "/".)
Help on the Subject of sfc:
Using System File Checker (SFC) to Restore System Files
You can run this scan more than once, assuming it runs at all . Sometimes it does take a couple of passes to catch everything. IF the system can find the error with the sfc, it will attempt to fix it. You only have to pay attention to the logs and such if something cannot be fixed.
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If you cannot run your Anti-Virus program, then something is wrong -- and you do realize this already, I know.
You might try opening up the folder in which the AV program actually resides and running the Anti-virus from there.
Reinstall the OS
You might be best served by making sure your latest backup is up-to-date, perhaps making a second USB copy of your really important files AND then making another copy of the data to another USB stick to be SURE you have everything... After you are as protected as you can be in this situation, then just Use your Reocovery Discs, Recovery Manager, whatever is still working -- and reinstall the OS.
Good Luck!