Windows ME does not come with a startup disk. You're supposed to make one. Most people don't know that. You do have a floppy drive, right?
You should be able to download a boot disk here. Use the ME OEM.
One of the biggest problems with ME was that they attempted to pretend that DOS did not exist. There is no way to boot to a command prompt and perform file work as there was in Windows 98. Except, of course, the boot disk.
Once you've made the boot disk, the computer needs to be set to start from a floppy first. Most older computers are already set this way. So you would insert the floppy, start the computer, and wait until it boots
Once booted, it will only show a black screen with a DOS prompt, which looks like this:
Once you've got to that point, you should follow the instructions here.
Note the second method, which shuts off your System Restore. That would also work. However, you will lose all restore points and essentially start from scratch.