Rekordbox 4 un useable

hi guys,

I bought a brand new iMac 5k last week and today i have installed the new Rekordbox 4. I originally imported me old rekorbox library and found that Rekordbox was completely un useable.

it lags and its nearly impossible to scroll through my library because its unresponsive and jumps all over the place.

i have noticed in the top right corner that rb4 has a cpu usage and this is constantly at 100%.

I decided to completely uninstall RB and all of its libraries so i thought i would start a fresh thinking it would help........it didn't.

Even with no songs in my library and with nothing analysed RB CPU in the top right is showing 100%??????????

Please can you help me with this issue, i need RB for doing but I can't use it as it is completely frustrating me overtime i open it up.

System details:

iMac Retina 5k 27 inch
OS X Yosemite Version 10.10.5
3.3GHz intel Core i5
8 GB 1600MHz DDR3
AMD Radeon R9 M290 2048 MB Graphics.

Many thanks in advance for your help :o)