Got a Dell PowerEdge that you replaced the motherboard on, and now it doesn’t have a service tag? Reset it with the asset.com tool, which I’ve conveniently packaged as both a floppy disk image and an ISO for those of us in need. They both use the Windows 7 boot disk DOS and asset_A209.com from ftp.dell.com (renamed to asset.com).
Once you boot from these you can set the service tag with:
asset /s <service tag>
You can also set the asset tag with:
asset <asset tag>
Or clear the asset tag with:
Standard disclaimer: your mileage may vary, and while I’m not actively trying to be malicious I take no responsibility for anything bad that happens because of your use of these. If in doubt call a professional.