Is your Mac Pro showing an issue like chime loop when it powers on? This is not a good sign. Such behavior signifies that your Mac is not getting any video signal at all. Your external display should show blank screen.
How bad is chime loop in a Mac Pro?
It’s not that bad as video replacement can fix chime loop issue. You can approach a local service shop to simply replace the video card. And the Mac will be back to its normal function again.
There are times failing processors may also give similar chime loop signals. But you will know it as soon as the service tech takes the video card out and starts up the Mac normally. This process should stop the chime loop instantly. It helps verifying that the issue is not corresponding to any logic board or backplane related issues.
Most importantly, failing video card is not a significant responder to allow logic board stay in chime loop. It’s the video card that is not functioning at all. As a result you will likely to see no display at all. External display will be blank.
What if the chime loop is not stopping even after the video card replacement?
The primary concern in this respect is the part number of the replacement video card. There are chances one may choose a wrong video card. This will not mitigate chime loop issue. The issue will stay right there. Getting the right and working part may resolve the issue.
A tech can remove the replacement part and test whether the part came faulty. Or a known good part replacement will give a correction. Whether the known good part is used or the replacement pulled out, the issue should go away. Then the Mac should start without such issue. Starting up the Mac without video card will prevent boot loop.
I have seen local service shops reworking on the existing video card and making it ready to work again. Eventually such rework fail. Therefore, replacing known good video card is the only reliable solution from a reputed service shop.