Mid-2010 MBP - Random shutoff, already replaced SDD and battery

Mid 2010 MBP running on Sierra 10.12.6.

So for several months now, my MBP will sometimes shut off while it's in Sleep with the lid closed. I'll be doing something like homework and close the lid for 5-10 minutes, come back, and it's unresponsive. There are times when the fan will start to kick in, but it's not too hot, and nothing comes up on the screen.

I've replaced my HDD for a Samsung SSD and swapped out the battery for a new one, but the problem is still happening. I would have to force shut down the laptop and boot it back up, which sucks when I'm working on something and have to open up programs again to get back to where I was.

I don't have the money yet to get a new laptop, so if there's any other way I can resolve this issue, please help! I appreciate any advice and can try to provide more information if needed. Thanks everyone!