External Hard drive connection?

[Kiz]

I'm not sure what happened but i usually connect my hard drive to one of my schools computers in the morning and it worked but when i tried to connect it later on today it did connect but every time i tried to pull up something it wouldn't open anything i tried to open up.Then when i got home to see if maybe i just didn't save what i was trying to open right and i plugged it into my PC it made the noise that tells you something connected but all that appears is this 'safely Remove Hard drive' window and It won't appear on my 'computer' help! please!! my School life is on this thing!