Help! Anyone any good at troubleshooting the steam client?

I'd appreciate any suggestions at this stage, am tearing what's left of my hair out.

Have recently upgraded my daughter's Samsung chronos series 7 np700z5a-s01 to Windows 10. After some teething problems getting the graphics cards and cache working, all seems okay. Apart from Steam. The client clashes following login. Have uninstalled (including everything in the steam folder), reinstalled, tried reinstalling in a different location, tried installing as admin, ran sfc /scan now (no problems), tried a registry clean (made no difference), tried the recommended procedure from steam support (some sort of cache flush - outcome no difference). Have now run out of ideas, I don't particularly want to regress back to the win7 backup before the upgrade, but am now seriously contemplating this...

If anyone can suggest something to try,I would be very grateful. A ticket has been logged with steam support, but they have not responded in the last 48 hours.

 

It might be a compatibility issue. Go to Stem folder, right click on Steam.exe and select the compatibility troubleshooting option.