Hello @Hasitha_2313015
Thank you for contacting the Instructure Community. We're sorry to hear you've been experiencing issues with using Canvas. It is likely your internet browser and we recommend clearing the cache and cookies or trying another browser.
In Chrome
On your computer, open Chrome.
At the top right, click the three dots
Click settings
On the left, choose Privacy and Security
Then, clear browsing data
At the top, choose a time range. To delete everything, select All time. I suggest at least 4 weeks
Next to "Cookies and other site data" and "Cached images and files," check the boxes.
Click Clear data.
If that doesn't work have you tried another browser, device, or app? Some schools restrict courses for a number of reasons - if you had the course before and can log in - click on Courses on the left and then All Courses. Do you see it here? If not you may need to contact your school directly to confirm enrollment and/or that the school settings haven't hidden the course from all students.