Hi Liang Kun,
Thank you for posting on the CostX Student Forum.
I will suggest you to uninstall CostX completely (without keeping database) and reinstall it.
For the reinstall, please apply for a new serial number at this link – https://education.itwocostx.com/support/forum/educational-request/ and then activate CostX with your new serial number.
If it is still not working, you need to uninstall CostX, uninstall antivirus and restart PC then reinstall CostX.
CostX Forum Admin