I believe you need a Torx screwdriver (star with 6 points instead of 4. Not sure which size). I managed to remove those screws with a 4 star one once, because Torx-6 is impossible to find anywhere here, but you need the exact right size and even then this can damage the screws badly, so I would avoid such solution. Try to find a Torx screwdriver somewhere and if you can't, you could try finding one online.

Did you try removing the batteries then putting them back in while holding down CLEAR, though? This lets you force a RAM reset. You can also try DEL which forces a OS re-install prompt. If the screen remains that way, then it might be the screen itself. I am not experienced in that stuff, though, so hopefully someone can help.

My TI-80 did similar stuff before when I last tried it. I didn't drop it, but it always remained somewhere in a huge stash of calculators, so maybe it broke it after a while. Dropping a calc might have damaged the screen too.

As for the CAS' do you absolutely need one? WOuld a regular TI-Nspire CX do the job? It's allowed at exams, unlike the CAS model, so you could try to get that in exchange.

If the screen is cracked, replacing the whole screen is the only option. It's possible the ribbon cable attaching the screen is damaged, but even Kerm (who has a master's degree in electrical engineering) had trouble fixing that.

The screws are indeed Torx-style. I have a set from Radioshack. Maybe they're hard to find in Canada, but there are a few stores selling them here in the US (subject to regional variation).

Kerm doesn't have trouble replacing Ribbon cables on the 83+. He fixes those all the time. It's the 84+ he has trouble with, since the cable is much smaller. It's about 30 AWG wire spacing, from what I understand.

See this post on cemetech.

DJ, you can use standard flat screwdrivers inside the torx set.

Oh, by the way, that's almost definitely a ribbon cable problem. Doesn't sound like a cracked screen at all. Cracked screens are more easily identified by the fact that they leak fluid. It's a fairly distinctive effect.

What you're seeing, from what I understand, is a communication problem between the LCD's driver and the display itself. (Well, sort of, the hardware is kind of complicated) Point is, the symptom you describe is a classic example of ribbon cable failure.

This actually happened a long time ago, I believe it (may) have been dropped?

didn't know that was even possible to break such a calc, mine survived many drops also a two story fall at school and still working oke. (not that i did those things intentionally to my calc)