Some common causes of not being able to check your results online with possible solutions are discussed below:

Website Technical Issues

Temporary Glitch: Perhaps, the website is going through some technical hitch. Just refresh the page, and you will be fine; or wait until later in the day.

Server Overload: It may so happen that a number of students are trying to log in at the same time. The server becomes slow, and it fails to open the results page. Try again later when less students are logging in; or try it off peak hours.
Wrong login details: Recheck the roll number, registration number or any other detail.
Delay in Result Declaration:
Results may take some time sometimes due to re-evaluation or some other administrative activities.
Keep an eye for the website or contact school for the updates
Networking Issues:
Make sure you are having a good internet connectivity. Slow internet or not stable internet can also deny your access to the result page.
Troubleshooting steps:

Go Through the Official Website: Access the official examination board or institution website to provide guidelines on how you may check your results.
Examine Board Helpline Center: Contact the helpline center of the examinations. They must have specific instructions and methods of checking for the results.
Find Your Educational Institution: Search around in your school or college. They may be equipped enough to provide information pertaining to date declarations and alternatives for checking one's result.
If you are still unable to figure things out, don't forget to ask your teachers, parents, or any other caring persons for help. They may have more tips or recommendations for you.