dash/hyphen when I type colon

Can you type the colon character when in a text document or email or is the problem everywhere?

If everywhere try the following:

1 - Reset NVRAM or PRAM on your Mac - Apple Support 2 - 3 times in succession.

2 - if still present boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and see if the problem persists. Reboot normally and check again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

sceerik wrote:

Why is my iMac suddenly typing a hyphen when I am hitting the colon key (shift/semicolon)?

Sounds like you may have the wrong keyboard active. Go to system preferences > keyboard > input sources and make sure there is only one item on the list, and that the name of that item is "US".

Did you receive a warning dialog from the Finder that looks like the following when attempting to use an illegal colon character in a file or folder name?

The reason for this is the Finder internal HFS file path construction uses the colon as a path separator character.