My iMac 2008 model starts up with a greyish white screen with a folder with a question mark in the middle very often, how do I fix that?
That’s an indication that it can’t find the System folder. It could be hardware (failing hard drive) or software (wonky OS). You can do an Archive and Install of your OS to rule-out the software. If that still doesn’t work, you may be looking at a failing hard drive.