If you're trying to sell it, then I'm assuming you don't care about the data it contains. I'd suggest you attempt to wipe the entire HDD/SSD, including windows, then re-install it via a USB.If that doesn't work, then your SSD/HDD might be having issues, so just get it replaced and re-download windows on there and you should be good to sell it.
Hi,   I am having all sorts of trouble trying to Update Win 10 to the 21H2 feature.  It says there is an error so won't install it. It seems to be the only update that it won't install. I tried a Reset keeping files from within the PC and as a DVD boot but it gets to the opening white 'Getting things' the panel disappears and that's that. Other times it gets to 9%  but hangs there for days. Is anyone else having trouble with the T7500 updating Win 10? I am trying to get it ready to sell so need to have the latest Win on it. Any help please?   oz    
T7500 Trouble updating Win10 x64 Pro to 21H2