I deleted my public key from the key ring.

I imported the key again

The key shows in th eOpen PGP Keys Screen but the key does not show up when I try to sign a file.

Good morning Thom,

OpenPGP studio does not allow you to sign files with a public key, which is why your key does not appear in the Sign and Encrypt and Sign options. You will need to use a Private Key to sign a file.

Please let me know if you have any other questions. :)