hit ctrl alt del and get rid of any programs that are using the files...
Run an antivirus to get rid of any viruses,

One other thing, right click the recycle bin, click on properties, do one of two things
A) make sure you have enough space for sending your files
B) check the box that says do not move the files to the recycle bin, remove them immediately

question is it just AVI files? Is it one AVI file in particular?
What software do you have installed?
BB