Micromax A121. couldn't access the internal SD card whenever I try to open gallery, rebooted several times. I lost some of the files and data due to this . Can anyone help to take the corrective meassure
the problems you are experiencing are related to your device software. I hope they release updates for you as this will fix the bug issues you are having.
For the time being I would suggest:
restarting your device, safely removing SD card and re inserting, pluging your phone to a computer and unpluging. Do this over a few cycles untill you can sync your SD card.
Another option would be to save your SD card files to your computer, then formatting the SD card with your phone. Afterwards proceed to moving your files back to your SD card. Although you will see results more with this method I would not recommend this unless as a last resort. Also be careful as this method can wipe your data.