how to downgrade my windows OS from windows 7

you might have some malware on your computer.

how to check and remove safely?

i did repair yesterday by pressing f8 and also fixed mccaffee whose firewall turned off and ran full scan which did not find any virus though. I hope mcaffee full scan check for malware as well. After repair i noticed once the windwos explorer did not close. But i will do more testing today evening and let you guys know.

i tested still windows explorer is closing abruptly. I think i have to downgrade to factory default. Hopefully that is only option. But i have 300 GB of data not sure where i back it up

If you don't already have a cloud backup service, you should get one.  I recommend CrashPlan for home users (crashplan.com) from code42.  Bsiness users should use inSync from Druva.  Crashplan free allows you to backup to some other computer or drive at no cost to you.   (do you have a friend with extra space on their harddrive?).  Or just buy an external drive - they are cheap enough.  Do you have a USB 3 port?  USB 3 would get it done much faster than USB 2.

Check out this article on cloud backup and this one on backup.

Crashplan  how much space they give for fre?
usb3 only i think. How to confirm?

300 Gb  backup?  buy a 1,2 or 4 TB disk drive  -they are cheap nowadays - around 60$

Look at the port. If it's blue it's USB3.  If it's not, it's USB2.

This issue aside, if you have 300 Gig of data and it's important to you, you need to back it up.  At the minimum get a portable USB drive.  As stated above, they are very affordable.

Backing up your data should be the first thing you focus on.  Otherwise, you could be looking for help on how to get your important data back on a crashed drive.

In terms of crashplan they give 0 space free.  The free portion backs up to a local drive, USB drive, external anything, or another drive of a friend. For a family it is 145 for unlimited cloud storage. (Cheap in comparison to what you would pay if you were hit by Ransomware)

I have about 2tb of data in their cloud. I also backup to a local drive.  All are versioning backups.

300 Gb  backup?  buy a 1,2 or 4 TB disk drive  -they are cheap nowadays - around 60$

4tb i can get for 60$?  I like usb passport type not electrical type?

i meant an internal drive; external ones cost a bit more

you said :"I hope mcaffee full scan check for malware as well."  they don't specifically look for them
so best run the 2 scans i suggested aswell