Laptops

At that time I noticed spells When the computer was very slow for 3 or 4 hours. At first thought it was a slow internet but for the past few days it has been occurring offline. This morning I tried to check my email and It was so slow to connect that it stopped responding. I tried other desktop icon with the same result. I tried re-booting and it took nearly 5 minutes to shut down. It took at least that long to boot back up. I finally gave up.
Two months ago I upgraded from win 7 ult to win 10 pro.the transition was smooth and it has been working well so I don't think it is the OS. Any ideas?