My Sandisk when plug to the computor it just blank and will not mget to the manual

Hello Sir.
In that Case You shud Upgrade the Firmware of Your Sansa.
Please Click on the link below to Download the utility and instructions.
Sansa View Upgrade Utility

Ask Me if You need anything Further budd.

You can format the sandisk and check it

First reset all settings top defaults settings.

Then press power button for 10 seconds.

Then remove battery and memory card from it.
Clean both battery and memory card.

Then refix only battery start your sandisk without memory card.
some times memory card has issue and this happens.Let me know.

From your statements i was able to understand that you were unable to access your device through computer(i.e your computer doesnt recognize your device.) but you should be able to access your device without connecting it to the computer.( i.e normal listening to music)..now coming to your problem, it happens if you unplugged your device accidentally from your computer while you are transferring music or files to it.so we need to generate a system file.you can follow either of these instructions 1. if you have voice recorder in your device then record your voice and save it as a file. 2. if you have fm recording then do the same process of recording and saving. both these processes generate the system file. your computer will recognize your device now.however if you are unable to view the file or unable to switch on the player or device at all then you have to replace the batteries

Take the battery out and put it back in
You might need to reset the player...of course you will lose your data but by resetting, you should be able to get the player working again. You need to press the power button for at least 15sec to reset.