my free memory in my mac s almost around 100gb
Memory or free disk space? Not enough available disk space can slow the startup disk down.
Right or control click the MacintoshHD icon. Click Get Info. In the Get Info window you will see Capacity and Available. Make sure there's a minimum of 15% free disk space.
Try a different mouse.
Welcome to Apple Support Communities.
If your CPU usage is 95-98%, you've got some app process(es) working hard!
Does the fan become loud?
What does Activity Monitor show?
(Click to sort %CPU in descending order as shown.)
Have you tried all of these things?
Safe-mode Boot: http://support.apple.com/kb/HT1455
Reset SMC: http://support.apple.com/kb/HT3964
Reset PRAM: http://support.apple.com/kb/HT1379
Repair Disk Permissions: http://support.apple.com/kb/HT1452