Computer Has a Virus, Cannot Get In

Hi, without trying to address the virus aspect, are you aware F8 is obsolete in that context and no longer supported? Why?
a. Fast startup
b. Faster start up times mean there's not likely to be time for the user to hit the key quickly enough.
c. introduction of automatic repair

Here's how:
Safe Mode - Start Windows 10 in - Windows 10 Forums

Note:
a. In the Tutorials, you can add safe mode to your boot options, so you would always have that as a prompt with a timeout after a startup.
b. People have posted how to add F8 back. But if you use SSD not HDD. I'd suggest there's little point - 12s or so from startup to the lock screen.

Comment: I would regard not being able to use F8 as indicative of a virus being present, even if I were using Win 7, the last OS to use F8 in this way.

Hi.
Simulating 3 failed startups will bring you into the Advanced Recovery Mode. Then you could get to a Command Prompt and enable the Hidden Administrator Account (Option #4):
Administrator account - Enable or Disable in Windows 10 - Windows 10 Forums

Once you have that account, you can either remove the password from your existing account, or create a new admin account without a password, to get you into the system. Be sure to hide the account when you are finished.

See here, Option #1, to get to Command Prompt in the Recovery Environment:
Recovery Environment - Use to Troubleshoot Windows 10 Failure to Boot - Windows 10 Forums

Once in the system, run some scans to see if you are indeed infected.

You can create W10 media using the tutorial here:
Windows 10 ISO Download - Windows 10 Forums

If you'd like to scan your system at boot, you can try:
Bitdefender recovery
Of course, you'd need access to another computer to create the media.

Suggest you d/l & use a bootable AV scanner on either a disk or USB. You have your choice of them here.

With a bootable virus scanner, you create a special flash drive or CD/DVD disc from a working computer and then use it on the infected machine to scan the hard drive for viruses - all without needing to start Windows.

15 Free Bootable Antivirus Tools (August 2016)

No, let's try to make it simple.

1. You can't boot the PC using its internal disk
2. You should be able to boot it from a bootable DVD or USB device
3. You need to do a virus scan on it.
4. Some AV manufacturers supply a bootable disk with an AV scanner on it
5. The intention is that you download and burn such a disk, boot your PC from it, and scan your PC.

That's always assuming that the problem with your PC is, in fact, a virus or malware... which we don't know.