amber flashing light and Error Code 2900:0221 from Dell diagnostics

Diagnostics failed because there is an error in your SEL log. If you clear the SEL using Dell Open Manage Server Administrator, diagnostics should pass. A PROC Machine Check can be caused by a number of different issues. If the issue is causing problems consistently, I would try to eliminate hardware by reseating components and/or removing any PCI cards or other components. Also, try updating firmware. Otherwise hardware may need to be replaced. Contact Dell support.