at the login screen, click on the power button in bottom right of screen
while holding shift, click restart
that loads windows into a blue menu at startup
lets see what safe mode looks like
choose troubleshoot
choose advanced
choose start up options
click the restart button
choose a safe mode (it doesn't matter which) by using number associated with it.
Pc will restart and load safe mode
if its a driver or program causing it, screen should be normal here.. is it?
Curious what it is like in a clean boot - you can do this from within safe mode
make sure to read instructions and make sure NOT to disable any microsoft services or windows won't load right -
https://support.microsoft.com/en-au/help/929135/how-to-perform-a-clean-boot-in-windows
if clean boot fixes it, it shows its likely a startup program. You should, over a number of startups. restart the programs you stopped to isolate the one that is to blame.
a reset should have fixed it if it was a driver... also if it was a startup program.
Can you take a photo and show us? need to upload to an image sharing website and showa link here
what are specs of pc?