A friend's Windows 8.1 pc cannot open any files, not even .exe, .lnk, etc. I suspect malware, but it's not something I've seen before and none of the standard tricks worked.
Symptoms
Regular Boot
Immediately on startup, a popup appears asking what program to run a .cmd file with. The desktop loads, but all links are presented as .lnk files instead of the usual and don't work. Windows+R works, but it can't start anything, instead asking what program to open .exe's with. This includes cmd.exe, sadly. The same is true for Metro apps, which show their start screen before crashing (including Settings).
Safe Boot w/Command Prompt
The prompt opens and I can run programs (e.g. regedit) from the prompt, but not through the usual interface. Starting explorer.exe shows the desktop (including broken links) and the task bar (without start button), but it does not start the actual file explorer.
Attempted Fixes
System Restore
There are system restore points to points in time where everything worked fine, so this seems to be the obvious solution. Unfortunately, while the process appears to run normally, it ends by saying it cannot complete because "it cannot access a file" (it doesn't say which). It suggests that this may be due to antivirus software, but that doesn't run in the recovery environment, does it?
Manually adding file associations
I opened up another laptop which does work correctly, in order to copy the HKEY_CLASSES_ROOT entries for .exe and exefile. The laptop has Windows 10 installed, but it's the best we had at the moment. Sadly, copying those entries did not work either.
The most important part of this, I believe, was setting HKEY_CLASSES_ROOT\exefile\shell\open\command\<default> to "%1" %*, but like I said, no change.
Resetting default file associations
Running the .reg files this Eight Forums tutorial had no effect. Which is strange because they appear to be comprehensive.
Startup Repair
It does not seem to be a startup issue, but I was getting desperate. Either way, Startup Repair does not run at all when invoked from the "Shift-Restart" menu (I'm not certain what it's called).
Proposed Fixes
I will be returning soon with an installation disk for more drastic measures. Here are the things I'm planning to try:
Offline SFC
The only reason I didn't try this already is because I didn't think of it in time. I'm not certain this will work, but it can't hurt to try.
Refresh
We did not have a recovery/installation disk handy, so this was not possible on my first visit. I've read somewhere that recovery disks can only be made on systems with the same OEM, however, which is not an option in this case. Is this true? Will a normal Windows 8.1 installation disk work?
Factory Reset
It'll be painful, but if nothing else works we'll have no choice. Any suggestions on how to avoid doing this would be most welcome.
Has anyone seen this problem before? As I mentioned, any solution that does not involve formatting the disk would be much appreciated.
