Black screen on reboot on windows 7

I’ve downloaded an obviously malicious file with a virus attached, but it was not caught by either avast or malwarebytes. When I restarted the computer it went through the start up and then goes to black screen, with nothing visible. I have started in safe mode but when I run malwarebytes the computer shuts off after about 5 seconds of the scan commencing. Avast itself will not run because it says there are no start or finish points.

Any suggestions please, and I’m not overly tech savy.

see instructions here https://forum.avast.com/index.php?topic=53253.0
scroll down to Farbar Recovery Scan Tool … run as instructed and attach the two diagnostic logs

I've downloaded an obviously malicious file with a virus attached
next time, check file you download here before you run them www.virustotal.com / www.metascan-online.com