According to the reference manual here, that blink sequence indicates a bad motherboard. 
Need advice. I have a Dell Optiplex 7050 USFF Micro-i5.Sometimes it has not been turned on again for at least 6H. The yellow code 2-1 flashes. It must be disconnected from the power supply, reconnected and only then can it be switched on. The outer feed block was replaced with a new one. The deep DELL test is passed 2x times. Where's the problem?
Any ideas?