They have successfully made my Garmin redundant after only 3 years, despite me paying for lifetime updates.
I have only skimmed this... that's my caveat. But... I read it as if you have successfully made your Garmin redundant. Can't you do what is suggested, get the update program successfully installed onto another computer and give it a shot?
My apologies if that's abrasive... you just sound so emphatically sure you've been badly treated, when it appears as though all avenues have not been investigated.
I have a Garmin, but frequently I lend it to my wife. It's never ever locked up or froze.
But I also use NAVFree On my cheap nasty samsung galaxy ace, and you can't really beat it on price. Okay on Long Runs you can be sitting on the motorway with the words GPS signal Lost, but I've never had an issue around town. It clearly does not use satellite, but more likely uses the location of mobile transmitters, of which there are more in town.
I tend to plan long journey's in advance, with a print out of the last 5 miles and ignore the sat nav until I'm lost. Once drove from Liverpool to Cardiff to Leominster via the A roads to avoid the longer M62, M6, M5, M50 and it wasn't until I was 5 miles from my journey end that it stopped trying to force me to Go East instead of south.