Are you running a 64bit version of your operating system?
i dunno, how can i tell ?
If your machine was crashing with your old memory,That memory might, be faulty,but putting in extra may just be masking the fault, I would remove the old memory and test it with just the new 'stick/s', you might find it runs even better than combining good with poss bad.Thanks for the replies , i just wondered if there was something missing from it, the extra 4gb of ram has made the computer much better to use , no crashing or freezing up.