Kernel panic with 1 long beep, need suggestions and helps on iMac 21.5

Question

First of all, my iMac spec is as follows.
- iMac 21.5 inches Mid 2011 (Intel Core i5 2.5 Ghz)
- OS X version 10.7.4
- Memory 4 GB
My situation is that I experienced a first ever kernel panic. It forces me to restart the system. I followed that, and then whenever it boots up a one time long beep sound occurs. After that a flickering screen (white and black) with normal chime sound occurs, and repeat itself for 3-4 times before actually goes into a normal login screen.
Everything is normal, I can use any programs properly. But one thing I notice is that "serial number" is missing in "About this mac" option. I strongly remember that it's there since a time of purchase this iMac. I also take a look at System/Profiles and nothing there as well.
I also take a look at the kernal panic log in /Library/Logs/CrashReporter and /Library/Logs/DiagnosticReports but can't find any relevant logs. There's just one file inside both 2 folders, and that log is dated which is not match to my incidence.
I tried remove out ram, and switch the slot between them, but it doesn't help.
Also I've tried reseting PRAM, but it doesn't help as well.
My iMac is within the warranty but outside of technical call.
Any suggestions and help would be very appreciated.

Answer 1

Contact Apple's Express Lane.
https://expresslane.apple.com/GetproductgroupList.action;jsessionid=KBdzQtTcydQS lvbJ6nthmsggQLWRJrXGh4phn9hb9vZNwqD0hJzp!-949435192