With that limited information, I can only suggest you start with a full reinstall by doing the following:
What version of Shotcut are you running?
Is this the first time you have used Shotcut, or have you completed other projects in the past?
You could try including the log file. In Shotcut select View → Application Log. Save it and upload here. Apart from the uninstall listed above, if that didn’t work, you could also try a different version from the downloads section.