My imatinon nano usb 4gb now only 1 mb what should i do?

It´s because it´s a secured drive, so it shows 1mb as public data, and 3,9gb of the drive is "secured" u can only reformat and unlock the secure partition with imation lock program, there you can remove the "secure" partition

I'd go into disk manager, delete any partitions and reformat the flash drive.