Why is high voltage coming out of HDMI port on my TV?
You mention that there were sparks and a concern about your ground, I'd check for an incorrectly wired outlet as a precaution. The initial check is a simple outlet tester. These have 3 lights and quickly identify a hot ground or swapped neutral/hot, along with other common issues.

What they can't identify is if there's voltage on both the neutral and ground, for that, you'll need a known good ground and a simple voltage tester. For a known good ground, you can find some plumbing lines that are grounded, or perhaps the ground rods that the panel connects to, but a really easy way is to plug a long extension cord into a friendly neighbor's house and use the ground pin (in your case, the bedroom is probably a good ground). Check if there's voltage between the known good ground and your ground, or your neutral.

Since you're seeing actual sparks, I'm going to rule out phantom voltage from running an hdmi near electrical wires. And since the problem happened after you moved the TV, either the TV was damaged in the move, or it's another device that you added to the mix. Start with the outlet to be safe, but if that's not the problem, you likely had a faulty device. Given the reading of over 300V, I'm guessing that it was a faulty device. A hot/ground short would usually trip a breaker (unless it's not really grounded) and only read 120V.