Windows 10 flashing screen - comp unusable

Alright, installed Windows 10 on my laptop just fine. Went to install it on my sons Dell laptop and get the flashing screen after entering his password. It actually started right at the end of the install so I held the power button and restarted. It keeps doing it once I enter his password and the desktop opens up. I've read that you have to hold the "Shift" key while starting to enter safe mode but this doesn't start in safe mode. The computer is unsusable at the moment (which is bad, as his school year starts tomorrow). Any thoughts on this? I've read this seems to be an issue many are having. Would love to just revdrt back to Windows 8 at this point but I can't even use the computer to see if I can.

Here is a number of ways to get into safe mode: 4 Ways To Boot Into Safe Mode In Windows 10

Do you maybe have a Norton programme installed on that computer? If so, uninstalling it in safe mode and then reinstalling that programme might solve the issue.

Thanks but I had already found that information before posting here. I ended up holding the power button to turn off the machine. Then when it was starting up the next time, I held the power button in again. The next time I turned it on, it said windows did not shut down properly and it gave me a series of options. One of which was to return to the previous "build". This took me back to windows 8, so I'm fine with that.

One thing I will say is this. I have Norton on all my machines. When I upgraded mine (HP), it automatically removed Norton for some reason and I had to reinstall it. On my sons Dell, the Norton desktop shortcut was still there so maybe you are right. I may go back in and remove Norton first, then try Windows 10 again at some point.

According to these comments 7 Windows 10 Upgrade Problems How to Fix Them it is most likely Norton and maybe really only Norton, which causes this issue. So uninstalling it might at least get you around that problem.

Open task manager ... under file (top left) "Run new task" ... type msconfig (yes it is hard to type as screen blinks, but it can be done) ... In the new box that opens (it may be behind the task manager box) go to Service Tab .... Scroll until you find 2 tasks that need to be stopped ... (1) Problem Reports and Solution Control Panel Support .... (2) Windows Error Report Service.... Disable these by unchecking .... Click Apply ... Click OK ... If you are prompted to restart, then restart computer .....
This is the main issue causing the screen to blink . .. Ironic that the items causing the errors are the solutions designed to report errors to microsoft