How to reset M600i?

Hi,
I need to reset my M600i (because it does not boot -
it starts booting, then resets itself).
So, I need to reformat the file system on C:
I tried SEUS, it successfully connects to the phone,
but refuses to upgrade it - it says that no
updates are available.
I almost gave up, but then found this site and studied
various threads all night.
It appears that powerful tools presented on this site,
like XS++, allow doing almost
everything with a SE phone - unlock, debrand, change color,
etc., etc., but my task is much simpler - I only need
to reformat or reflash the file system.
How to do it? I didn't find any instructions for that.
I tried running XS++, it connects to my phone,
but then what? I tried using FSX option,
but it XS++ crashes right after printing
"Activating filesystem".
Is there any other way to fix my phone?

Thank you
John