My sony eric. 750 keeps saying memory stick not available when camera lens slid open please help!?

I cannot access memory stick on my pc when connected with usb.
do i need this to download mp3 files?

Yes you will want to put your songs on the memory stick. Close the camera lens and it should fix the problem. You can also call Sony-Ericsson and ask for tech support to see if this is a glitch in your particular phone or a problem with the model itself. call them at: 1-866-766-9374