Did the machine name change? The default SID for 11g express is xe, and I can see in your log an SID for acmepos (clever btw). I had the same issue, and it was problem in the listen.ora calling to a improperly pathed SID. Not sure if I helped any. Forgive my noob'ness...db admin is very new for me.
What does the alert log say? copy and paste the content please