Is my MacBook Pro 15" mid 2009 dead?

My poor MacBook Pro 15" mid 2009 is about 8 years old now and for the past year I haven't been using it that much.

I tried to turn it on a few days ago and it was stuck on the boot-up bar for at least 45 minutes then it went to the file folder icon with the question mark.

I asked my friend and he suggested formatting the hard drive as I didn't have anything on it I needed to keep. So I bought the tools and hard drive enclosure and carefully took the hard drive out and put it in the enclosure and hooked it up to my desktop PC.

I got it formatted and made it an exFAT drive and it showed healthy and the full space available. I thought okay great this should work...well not quite! I reinstalled the hard drive back into the my MacBook Pro and it either has a plain grey screen with nothing showing or the file folder with the blinking question mark.

I tried command+r while powering up, I also tried command+s while powering up. I tried leaving it alone...nothing is working!

I know it's an old computer now and it had a good life but any suggestions what else I could try?