How can I fix my scratch disks and internet connection?

Have Dell "Expression" model, (I think, or something that sounds like it), desktop since 1999. Error box said: Scratch disks are full. Tried to empty a few files. Took off wrong one(s). PC now fails to connect with internet. Cannot find which one from "Recycle bin". How can I reconnect with internet and how do I stop scratch disk pop-ups? Pie chart shows D drive is full yet figures do not correspond. There should still be some free space. Pc was reset by teacher for D drive to be initial drive used. (D is smaller than C drive). C drive I have to switch into and has a third space left on it. I have tried to download files onto disc to clean all info off but lack of space on disc prevents this. Can anyone help with this problem please?