Windows 10: PC suddenly takes a long time on startup and is extremely laggy on the login screen...

Hello.I have recently opened up my PC to clean the insides as I haven't done it for a while. I had unplugged everything and went on with my cleaning. I did not touch anything inside except the top of my GPU to hold the fan so I could clean it. I did everything as carefully as I could and went back to using it. Now there was something wrong with my startup. It took a little longer as expected. Everything seemed fine when I booted it up. Then I opened up a folder and tried to open some more folders and suddenly the whole file explorer just stopped responding. Because of it I couldn't interact wi

:)

 

extremely long startup time

Started out with scanning and repairing drive C at power on. Then progressed to (47%) and froze. Taking up to 10 minutes to finally come on, and after doing disk cleanup and defrag, the computer working normal and fast. Restart is still very slow and after
doing a restore the scanning and repairing went away, but the login screen takes about 5 to 7 minutes to get through. Scanned with AVG and Defender with no results. Tried several remedies from internet search, but none seemed to help. Can you give me a step
by step instructions on how to remedy this issue. HP15 laptop, Widows 10. Thank you,,,,,,,BTW, I shut off the login but it still takes a long time to cycle through to desktop.

 

Extremely long and incomplete boot

This may be a long shot. My PC hung at boot yesterday after typing the password - see Can't Login - Further Troubleshooting Steps?

I ran chkdsk c: /spotfix and all is now fine. Someone has also suggested running chkdsk c: /r.

 

Windows 10 slowdown and extremely long boot time

Yesterday a HP ProBook laptop was running fine, with 8GB RAM and Intel Core i7-6500U 2.5GHz CPU.

Today morning, the Windows 10 machine was extremely slow. Windows task bar was not responding. Using some OS features line network manager wasn’t possible. So decided to reboot the machine. After rebooting, the windows got stuck at the loading page.

1. I hard-reset the machine, and used diagnostic tools, but they didn’t show any problem.
   
2. Pressing F8 at boot time, i.e. safe mode, led to automatic repair, which would eventually end up in a blank/black screen.
   
3. Finally, I rebooted again and waited so long for Windows loading to finish. After some long minutes finally Windows showed login page.
   

The Windows is still slow, but it is unstable. Opening an application might take more than 2 minutes, maybe 3 or 4 minutes.

This is NOT the first time I run into such slowdowns. I wonder whether this behavior is occasionally expected? How can I prevent such slowdowns?

Laptop has HDD:





UPDATE

Two days later:





Suddenly, I run into the blue screen. I wait long but it is stuck at 0% Complete. I restart manually. Restart takes maybe 15 to 20 minutes. Then I receive a login screen with no input field for password! I restart again, this time it's faster. I get a login screen WITH a password field. I login and opening any application takes 2 to 3 minutes.

As suggested by the accepted answer, probably I'm going to totally replace this OS =(

UPDATE

It is more than one month since I reinstalled Windows 10 and deleted all the old partitions which were MBR-based and created new GPT partitions. During this period, the new Windows 10 is responsive. I'm satisfied so far