Look at the Mi Max notification panel after connecting to PC.
From there click on the notification showing USB for charging connected, and change it to the one that allows file transfer (MTP).
Ok thks bro. Btw i came to know from the miui forum that unlock e phone is able to transfer data eg photos,media etc to pc via usb connection, but it may cause some problems on miui os after unlock.
Any bro did unlock and no problems on e phone?