We could use a little more information. What is the make/model of your computer? Is it a desktop, laptop, tablet, phone, etc.?
Does your computer have Win10 pre-loaded on it? Or did you upgrade from an earlier version of Windows such as XP/VISTA/WIN7/8/8.1??
It sounds like it could be either a problem with your Win10 upgrade, or if Win10 came new, could be a failing hard drive. Of course once you provide us with some information we can help you better.
The first thing to do is to test your hardware, and eliminate that as being the cause of your problem. The second thing is to try the common remedies for a corrupted Win10 upgrade or existing install.
Here are some things to try:
**TEST YOUR HARDWARE**
1. Check your hard drive with free SEATOOLS drive diagnostic. Run BOTH short and long tests to completion; if SEATOOLS returns any errors, then your hard drive has failed and must be replaced.
2. Check your RAM memory sticks using MEMTEST. Test each RAM stick individually for a minimum of 8 passes; then check all RAM sticks together, again for minimum of 8 passes. If MEMTEST returns any errors, that Stick or Sticks have failed and must be replaced.
**TEST YOUR SOFTWARE**
1. Did you remember to run the Win10 Uprade Assistant program from Microsoft prior to your upgrade? If not, you should restore your computer to the factory version of Windows it came with (Win7/8/8.1), and look for drivers and programs that are NOT Win10 compatible and remove them prior to the upgrade. After the upgrade to Win10, you can put those drivers back or the newer versions from the manufacturer of the device; for example check the website for the Graphics Card/Chip you are using and re-download it manually from the site; ensure to check the new Graphics driver has been tested with Win10. Do the same with any removed programs found to be non-compatible with Win10.
2. Have you checked for viruses and malware hiding on your hard drive? Use your built in Anti-Virus program if you are running one, such as Norton, Avast, McAfee, etc. Next, use the free MALWAREBYTES from malwarebytes.org and scan specifically for spyware viruses. Traditional AV programs will not find/remove all of these. They can drastically slow down your system if not removed. Lastly, download FREE Rootkitbuster program from trendmicro.com and check for/remove Rootkit viruses. These hide on invisible partitions on your hard drive and must be found/removed also. There are also new Rootkit viruses that only appear on Win10 computers. These are recent, and if you haven't used a Rootkit checker; they could be hiding on your hard drive and only cause problems with Win10.
3. Try performing a "CLEAN INSTALL" of Win10 on the computer you ran the online upgrade on. This requires you to reset your computer back to the factory version of Windows that came with that computer (Win7/8/8.1). You can accomplish this by using the built-in Recovery partition that's hidden on most modern computer's hard drives. If the partition has been removed by you or it's one of the computers that does not come with the Recovery partition, then the laptop maker usually provides a CREATE RECOVERY MEDIA TOOL with which you can make your own factory Recovery Media (DVD or USB stick). This program works best with DVDs, and that could take from between 1-12 DVD discs to do. DVD discs are cheap in bulk; around $0.20 each. Bear in mind that if you attempt to use the Recovery Partition tool, and you haven't tested your hard drive yet, there's a 50% chance or better that the Reset to the factory version of Windows on your computer will fail. (this is why I listed the **HARDWARE** section first above).
* Once you test your Hardware, and both your RAM memory and your Hard Drive are found to be healthy, go on to the 2nd section and test your Software.
Post back answers to my questions, and the results of the hardware & software tests. We will advise you further.