photoshop 5.0 agm.dll missing

It is a very old application, but the application itself may have become corrupted.
You have not written any OS or hardware information, so you may not be getting the correct information. As for hardware and OS, there is a possibility of HDD or OS trouble as they are reasonably old.
Personally, I think you should consider getting a new PC and a new Photoshop plan because of the security risks involved in continuing to use an OS and applications that are no longer supported.