Assuming that you're using Windows 10, follow this path for your HP problem:
Start > Settings > Printers & Scanners > (Name of printer) > Manage > Printer Properties.
You should then see a 'Maintenance' tab, or similar. Click on it. There should be a 'Cleaning' (or 'Head Cleaning', or similar) button there and possibly a 'Deep Cleaning' one too. As your printer hasn't been used for ages, I suggest that you should probably go straight to the 'Deep Cleaning' button, if there is one. (If there isn't then, obviously, use the normal 'Cleaning' one instead). Click the button to clean the print heads. Then look for a 'Print Test Page' button and use that. If the problem hasn't cleared, repeat the process until it does. (I've sometime needed to clean the heads at least half a dozen times before the problem has been fixed).
For your Canon problem, turn the printer round, so that the back of it is facing you. Then pull it towards you, so the nearest 10cm or so is overhanging the edge of your desk. There's a fairly obvious lever there. Pull it to release the mechanism, allowing it to drop down below the level of the desktop. Get a torch and look inside. I suspect that you'll find that there's a very small corner of a sheet of paper (probably less than a square centimetre) in there somewhere, which you might then need tweezers to remove. (Written from repeated experience with the same series of printers!). Removing it should solve your problem.
Good luck!