I have some more information:
After I run Modal Analysis, Ansys stores the following info at "dp0 ->SYS->MECH":

But as soon as I run Random Vibration analysis, they delete all these files:
Now, if I see the solution information object for the possible errors, I see that Random vibration requires the file named "file.dp", but it has already been deleted when I ran Random Vibration analysis.

I have no idea what is happening here. Would you please help me?