Kindly let us know if this problem occurs with part template only or it occurs with new Assembly template also.
It may be an issue with your graphic card driver.
To check the same :
Open your SolidWorks.
Go to tools>Options>Performance.
See the option "Use Open GL" is checked or not.
If it unchecked , check the option.
Try opening your part template.
I hope it helps.
Thanks & Regards,
I had this problem earlier today, and that option of 'use software OpenGL' is grayed out. BUT restarting the computer fixed it.. just in case anyone else has the issue.
Checking the Use Open GL option solved the problem for me. Thanks!