I put in a lot of music

Now every time I power up it says to remove 90MB and then it shuts off.

It is a common problem. Some of your music files are corrupted. Search the forum for information.

Here’s the SanDisk Knowledge Base article on the subject:

http://kb.sandisk.com/app/answers/detail/a_id/848/kw/Not%20enough%20room/r_id/101834

I found a way to format it and now the problem is fixed.