Just how are you starting this HTA? By double-clicking on it in Windows
Explorer? If so, does the .hta filetype has a handler associated with
it? In a command shell, when you run:

assoc .hta

what does it tell you is the filetype handler? Is it htafile? If so,
what is the "open" action defined for the htafile filetype? From the
above command, you should get:

..hta=htafile

Then you go into the registry to find what actions are defined for the
htafile filetype. In regedit, go to:

HKEY_CLASSES_ROOT\htafile\Shell

Under there should be a subkey for the action, like "Open" under which
is another subkey called "Command" for the command to run the handler
for that filetype. So under:

HKEY_CLASSES_ROOT\htafile\Shell\Open\Command

what is the default data item's value? I have:

C:\Windows\SysWOW64\mshta.exe "%1" %*

That means the .hta file gets passed as the first replaceable parameter
in the command line. They've enclosed it in double-quotes just in case
the path to the .hta file or the filename itself has space characters.
The %* means to pass the remaining command line parameters (but notice
it isn't enclosed by double-quotes). If double-clicking on an .hta
file, I would expect only the %1 to have a non-blank value, anyway,
which is the path and filename of the .hta file on which you double
clicked.

Is the mshta.exe found in the path specified in the registry for this
handler? If you cannot see it in that path using Windows Explorer, use
the attrib.exe in a command shell to check if the hidden or system file
attributes were set on it (they shouldn't be). Some rogueware does this
where it first sets the hidden or system file attributes, or both, on
many files, might rename them, and some nasty rogues (ransonware) will
encrypt the file(s) and hold them for ransom until you pay for their
"anti-virus" program to remove the infection (that is their doing).