Black display when switching customers

Hello I’m new to this web page, supposedly a pc skilled [for those I get it right, those I don’t, I hate to think what they say]
My spouse is studying her Phd in legislation and the pc provided by means of the College can not take care of the weight, so she has hijacked my desktop.
Dell 990
Win10 professional 21H1
Processor i7 [email protected]
RAM 16gb
Garage 4TB + 32TB NAS
Graphics Nvidia GeForce GT730 Show Dell P2714T
Bios Dell A24

There are two issues:

1st When switching customers {each Admin} or signing off consumer, the show is going black and remains that manner till the show is became off and the on once more.

second Microsoft Phrase 365 moderately steadily scrambles the display, she has a number of paperwork together with PDF’s open on the identical time { 20 -30 paperwork}
alternatively open some other program on the identical time and it show is okay.

any lend a hand, recommendation and hints gratefully won
.