​ ​ The flash drive that have been used to save the datas and suddenly the datas from folders are not opening. 

It means the flash drive are just have power on and have seen the folders only. So with these scenario, If it is normal and can be accessed, then there must be something wrong with the first port. The first step to do If in case it still does not work, then connect the USB or Flash drive  to another PC's USB port, just to check if the  USB stick itself is dead or your PC goes wrong. Try again to insert your Flash drive into another port on your PC and check whether it is accessible. Then if all the trials are still same, contact the Data Recovery establishment to get you help before anything else may happen. Just always bare in your mind don't ever do to format  any device that has data's on it. Because  formatting is  not the solution to make it work your data. Additional reminder if this is happen to the flash drive, don't ever think to reuse this flash drive because surely may be back the problem. The Data Recovery Center even will not going to use the once damage drive, once the client approve the amount to pay. They will extract the datas into new storage. 

One of our new client encounter this issue and we have been solve the problem immediately with the affordable price.