Slow to begin, but working fine after. Hardware problem?

Hello, I hope you can help me.
I have a Samsung Q530. It is quite dated, I think possibly almost 6 years old, but I love it and would really like to keep using it for a bit longer.

Problems started a few months ago (around October). The computer started being really slow, particularly Google Chrome which, until then, had shown no issues at all.
Long story short: I tried many different methods, starting from reinstalling Chrome, then running antivirus scans, including in safe mode, even tried to update it to Windows 10 hoping it would fix the problem, but it didn't. I did endless google searches but to no avail.

Two months later, in December, I decided it was just a lot easier to reinstall the OS, and so I did.
That seemed to finally solve the problem! Everything was working fine again, back to normal.

However, it has now been a couple of months that the laptop is slow again on start-up - and by this I mean AFTER it has booted up and I have entered the password to log into my profile. It would open up my profile, and then I would click on Chrome or on a folder and it would take a good 10, 15 minutes before the computer responds again. But after that time has passed, it does work absolutely fine.
I have already checked for programs that open automatically at start up and there's nothing suspicious or extra.

On one single occasion, it took a while to show my profile after I had put my password in, and I eventually got an error message saying that my profile data couldn't be found (it had opened a generic user profile). I restarted it immediately and it then logged me on fine.

I tend to exclude a software problem, since I have just formatted the whole machine and I haven't even put my data back on yet. So, it is with dread that I ask: might it be a hardware issue? CPU, motherboard or hard drive too old perhaps?
I understand it is very difficult to say but any pointers, any ideas from you experts would be very helpful.