If you can read the card on other Windows computers but not on one specific Windows computer, the most likely reason is that the card reader on that computer has failed. This is not an uncommon event. If you have another SD card of the same type, see if you can read files on that card. If a second SD card also cannot be read on the computer with the problem, it is even more probable that the card reader on that computer has failed. In this case, you can buy an inexpensive USB-connected card reader. Just be sure that whatever reader you buy is capable of reading the type of cards you have.
If you can only read the card on a non-Windows device, such as a camera, the card is probably formatted using a file system that Windows does not recognize.
If you can read the card using another computer, you could copy the files from the card and then attempt to format the card. This may or may not solve the problem.