need help with imac

[Bully]

Imac 2.4 ghz 250 hard drive
I just installed 4 g of 800mhz crucial ram and my computer is reading it but after about 1 1/2 min it freezes and half the screen will be blue and t makes this wierd sound does anyone have any idea what this is

And yes it does say on the menu about this mac
2.4 ghz
4 gb ram 800mhz

[Catamer]

i suppose you could have a bad stick of RAM and just need to find it, or it could be something worse like a weak or in the way out power supply.

make sure all of the memory is identical ( like 5-5-5-15 ) mixing and matching is NEVER good.
try removing half the memory and run for a while see if it still has the problem.
then try again with the other half of the memory installed and see if it still has the problem.
if it's just a single bad stick of memory hopefully you can find it this way.