Press F2 and make sure that the OS install mode is disabled. That will limit the memory to 256MB. If that works add a 2nd stick back in. 
I have a dell poweredge 1850. I booted one time and it booted fine. Then I powered it off by pressing the power button on side. Pressed the power button again and then when it boots, it displays the following information:  Dell Systems PowerEdge 1850 www.dell.com Memory mirroring enabled two 3.20 ghz processors, processor bus: 800 mhz, l2 cache: 1mb  and then it gives me a blinking cursor. And it just remains as a blinking cursor.  What can I do? 
Blinking cursor when booting a poweredge 1850