If I try to enter a password at the login screen or press the power button, Windows freezes up. Therefore I cannot restart in safe mode.

When your computer hangs, or freezes, it's disruptive and can slow you down. There are a few reasons your computer might hang, freeze or crash.

If it freezes during startup, you can perform a startup repair. If it freezes randomly then you need to install all the Windows Updates. Computer freezing due to virus issue can be resolved by doing a Scan with Microsoft Safety Scanner.

Check the link mentioned below and see if it helps in getting the issue resolved.

Windows 8.1, Windows 8 or Windows 7 hangs or freezes

Note: The Microsoft Safety Scanner expires 10 days after being downloaded. To rerun a scan with the latest anti-malware definitions, download and run the Microsoft Safety Scanner again.

The Microsoft Safety Scanner is not a replacement for using an antivirus software program that provides ongoing protection.

Please take a backup of the data to an external disk as scanning may result in data loss.