Have you ever tried a triptan, like imitrex?
I would go to the doctor, to rule out rebound headache. This could be the culprit.
propranolol is a beta blocker used for the prevention of migraine. If you don't have rebound headache and it is just the propranolol losing effectiveness your doctor may increase your does (40 mg isn't all that high), or switch you to a new drug. If propranolol did work for you for a few years, you might want to try another beta blocker that is used to prevent migraine (e.g. metoprolol).
Yeah, computers can be killer. There are a few things you can do to help alleviate the discomfort caused computer use. What type of screen do you use (CRT, LCD or LED)? Are you photosensitive at all (other than from a computer)?