Upgrading from Win 7 to Win 10.

I get the Win 10 download and the notification saying you are ready to upgrade. I accept and proceed to upgrade.
The PC check says, my pc which is a Dell XPS L502X (probably 2012 - dont remember the year) is ready and will have no problems.

The upgrade starts; goes through reboots, copies the files; reboots; installs features and drivers (the next step is the configuration); reboots and then presents me with BSOD with the error "SYSTEM_THREAD_EXCEPTION_NOT_HANDLED". No other information in brackets. It reboots, attempts to recover installation, reboots again, presents the same BSOD again, reboots again and restores my Win 7.

I thought it might have been with NVIDIA or RealTrk drivers - I uninstalled them and replaced with standard vga and audio drivers; but no luck - same process & error.

The original Dell had a 1TB hard drive. I had cloned it to a 500GB SSD about an year ago and replaced the non-ssd drive with the SSD drive.

Can anyone help? Any ideas?

Thanks so much.