You really don't need a service tag on a old model. That's for computers still under warranty in case support is needed. Your old tag is gone now. It was on the old board. Just use the model number for parts or help from users here in the forum. Include your operating system when posting.  
I purchased a replacement motherboard from eBay as I had no warranty on the device and they didn't give me a service tag number so I am stuck and the service tag utility screen if I put the service tag associated to my computer will it allow the computer to boot up or will it lock the motherboard, I am also awaiting a response from the seller. 
Precision 5560 service tag utility screen