What would cause this? A virus? A glitch? Ive tried wiping and starting from scratch, and it still resetts occasionally. Please help.

It's not a virus. Could be a glitch.
Most likely culprit is the microSD media card.

Try removing that, and see if the reboots stop.

Ive tried that, and it still restarted. Could it be b/c of a ringtone? VZW told me it was the contact list, so I wiped and typed in manually every contact. And it still restarted.

sounds like the battery is coming lose, losing the connection and rebooting the phone.

Ive used two different batteries and the same result.

Do you have any 3rd party apps?

No 3rd party apps.

Yes, but if the slot the battery goes into is the problem it will still allow any amount of batteries you try to come lose.
Stick a bit of card (usually a business card) between the battery and the back cover. stick it to the inside of the back cover, and see if that fixes it.

Ive used 2 different batteries, one regualr battery and one extended battery....And ive used two different BB curves....I think its something with the media card/ringtones

I have an 8310 that did the same thing and was told it was a hardware failure. Sent it off to the BB repair shop last week and hopefully get it back tomorrow night. I'm starting to wonder if that was really the problem as I'm seeing this kind of problem pop up in the forums a lot lately.

happened to me with the 8300... flashed if with the new os and it never happened again.

How do I do that? Where do I get the new OS?