Lagging of Minecraft, although the computer is new

Please bear with me. English is not my first language! I recently bought a new computer, which has the highest spec, but my Minecraft is lagging. I think, it has something to do with my java client.
I downloaded the X64 java client. Then I installed it, but my MIC is not working. So, I tried with X32 client. It works with this, but the lag is awful and unplayable. Do you know why the X64 doesn't work? My problem is very frustrating.

Error: No JVM could be found on your system. Please define EXE4J_JAVA_HOME to point to an installed 32.bit JDK or JRE or download a JRE from www.java.com.
