I opened up my PC and i went onto steam and it said that all of my games needed reinstalling. Then i clicked on them and it said that it could find disk space. Then i opened file explorer and i saw that my D:\ Drive had a blue question mark next to it
and i wasnt able to open it .
Open Disk Management (accessible by right clicking your Start Button)
Right click the partition on that drive and choose to assign a drive letter, assign a letter that is not in use like F and apply that
Restart your PC, check to see if that question mark is gone, then go back in and assign the letter D to that drive, restart your PC and Steam should see the games again . . .