Its not even finding your HDD..if its was, it would tell you
'NTLDR not found or missing'
If your just getting the DOS prompt, that means your mobo is not seeing the HDD as operational. Try changing the IDE setting from 'compatible' to 'enhanced'...something just changed when it cleared Cmos...you just have to figure out what.
*Try it will only one stick of RAM and then the other..just for 'ish and giggles.