When my Mac Pro starts up the line goes through then it ends up showing me a circle and line through it

The moving progress bar is telling you it is loading things up and making progress.

The prohibitory sign says that some components of Mac OS are too damaged to be used, and you will need to re-install MacOS. That can generally be done with a re-Install-in-place, BUT: that process re-writes over 350,000 files. If your drive is dying, that much re-writing could send it over the cliff into never working again.

Do you have a Trusted Backup?

--if yes, feel free to re-install.

--if no, consider obtaining another drive and re-installing on the other drive in an External enclosure, then using the full power of MacOS to "rescue" your files.