1 press"alt+tab",come back to desktop,and press again ,go back to game, but it is crashed.
2 set the resolution to "640*480",then exit game. and my os halted.
3 modify option in the menu.exit game. when start game next time, the option goes back to default.

I'm not sure I understand fully what you are saying, but it sounds odd. Alt-Tab does sometimes create problems including CTD's and freezing PC's, but I've never seen this happening with Morrowind.
I'd say uninstall Morrowind (back up the SAVES folder first) and then re-install it. If it's important for you, try Alt-Tab before installing any mods.
You may also consider checking your registry after the de-installation, just to make sure there is no Morrowind-related garbage left (but only if you know what you are doing - editing the registry has the potential to create problems which are worse than the ones it's supposed to fix, if not done properly).

Is this a Vanilla install or is it modded?

I ask because if you use Morrowind Graphics Extender XE
(allows MW to utilize many graphical over Vanilla MW but I'm thinking of the non 4:3 resolutions you would likely need to use "fake full-screen on a win 10 setup)
you could probably use a "fake Full-screen" utility
(Fake full screen seems to help some games that have "alt-tab" issues)

I did not install any mod. just the Elder Scrolls III: Morrowind GOTY Edition.
I also play this game on windows xp on another computer. It works well.