I had a similar problem in that my monitor display was restricted to Microsoft generic and the screen size was restricted and graphic icons distorted.
I eventually solved the problem by searching for Device Manager. I identified the problem Display device (same yellow triangle indicator as previous Windows versions) and selected update driver and 'search my PC' (Not search the internet). My graphics card is NVIDIA so I then navigated to the NVIDIA folder on my System Drive (C
located the drivers folder - Windows the automatically found the existing pre-upgrade driver. I confirmed the update request and the existing 'old' driver installed. The screen flashed and refreshed a couple of times, then the display appeared as it was before the W10 upgrade.
Note: when I attempted the search the internet Windows located the NVIDIA driver update for NVIDIA GeForce GTS 450 - but failed to install with Error 0x80070002 - I could neither manually download and install from the NVidia website, nor via Windows update.
This using the existing driver solution worked for me insomuch as my screen was restored. Interestingly Windows Update still reports that the driver fails to install!