Aurora R11, won't start up after replacing harddrive

I recently purchased a new Seagate BarraCuda 4TB Internal Hard Drive HDD due to my old hard drive failed.  I cleaned out the computer by removing all the dust inside before change the hard drives out. I attempted to start the PC but during the PoST it blink 4 times and then shuts itself off. I looked up the meaning for 4 power LED flashes and listed Memory or RAM failure. The problem is I didn't change the RAM but proceed to remove all 4 sticks of RAM and put them back in making they were seated properly. Again, attempted to start the PC but same 4 blinking power LED Flashes. I reset the CMOS by remove the battery and waiting 15mins before putting it back in. Still no solution to the problem. What else can I do to find out what is wrong given all I did was change the hard drive and clear all the dust inside the case?

Note: PC no longer under the warranty.

Thanks