However it now doesnt even want to turn on, as in I have swtiched it off, switched off the plug, left it off all night then this morning I turned it all back on again, the machine started up, the white screen with the applie logo came on with the wating circle symbol thingy.... then the screen goes blank, but machine is still running, then all the sudden the fan goes into hyper mode and is mega noisy and thats where is stays.
I have turened it off and back on again and it just goes straight to the blank screen and the fan kicks in....
this is very fistrating as I cant even get into the computer to see or change any settings.
This has all happened since I did the latest Lion OS update...
I would try doing an SMC and PRAm reset, if that doesn't work then see if it woll allow you to boot into recovery, once there verify disk permissions/repair disk permissions. If the problem presists from there re-install OS Lion (assuming you were able to get to the recovery partition.
Shut off machine > Pull out the power cord from the back of the mac > While the cord is removed hold down the power button for 15 seconds > plug the cord back in and proceed to boot
Hold down Command + Option + P + R > trun on the computer and continue holding those keys down until you hear the startup chime 2-3 times
In order to boot to the recovery partition hold down the option key at startup, a screen should appear that has Mac HD and Recovery, go into recovery. From there select disk utility and this will allow you to perform first aid (I.E. repair disk, verify permissions, repair permissions)
If that does not work, again boot to recovery and select "reinstall Mac OS X"