I cant play minecraft, i have done everything

Hello, so I have done EVERYTHING, to try to open my Minecraft today when I logged into my school computer i saw Minecraft on there, and it was fine but then, i closed it and now i cannot do anything i have mods on there a lot, and I've tried unstalling it, but that wont work. i have shut my pc down multiple times, I've restarted, turned my pc off but that wont work. when i go to reinstall it it just stops at half download, and wont go further, and when i cancel it it wont let me close out