System just freezes on crashing at various times of usage, and the memory is as follows: 512mb 256mb and 128mb all 133mhz.I tried changing slots but no joy.Could it be just too much memory ? almost 900megs.Presently running XP pro on Athlon 1.2 ghz system.. .I though it may be related to the inability to shut down the system normally through windows.When I try to close down it seems to hang on the final task then freezes.