meanwhile these guys are pretty good at their work/scam
whatever you do never download a tool from them.
In the end they will syskey you if you decline to pay their scam.
I've had quite a few senior customers fall for this scam. These fake Microsoft Support creeps specifically target the elderly, and as you say if someone doesn't pay they bork the system. I've sometimes been able to recover the O.S. by rolling back with System Restore if the creeps haven't deleted the restore points. Sometimes even with the restore points it fails with the system saying there is no admin account. Does anyone know how they do that?
My mother fell for it a few years ago and got her PC borked. First thing she did was ring me and ask what she should do. I told her to unplug her laptop and remove the battery, that I would sort it out when I got there. It was easy to sort out because the machine was running like a hairy goat and needed a reformat anyway, so that's what I did and all was well.
The [fake] MS guy told her that he could fix it for her if she was willing to pay AU$360.00 and provided her credit card details to enable the payment. Now that was completely the wrong approach. She told him she had no money [which was a lie, she always has plenty] and promptly hung up. She's one old bird you don't try to con/get money out of. She's as tight as a fishes arse will only part with money if and when she sees fit [which isn't often] and NOT before.
As for how the scammers do that, well they get the PC user to allow remote access, and from there they can pretty much do anything they want... like disable the machine and 'passively' demand money to fix it.