Not able to see all core after upgrade in win 7and win xp on esxi 4 n 5

i am using win 7 Clone and win xp clone  on vmware esxi 4.1/5.0/5.1 and but after upgrding CPU core 2 to 4 not able to see all 4 core in guest OS same thing working on server OSbut not in client OS . can we have any workaround for windows7