cached memory and free command

I have a 2 cpu server running SLES 11.4 x86-64 and it has 1.5 tb of RAM. >free -g total used free shared buffers cached Mem: 1514 284 1230 268 0 269 Running a number crunching software, which has worked fine in the past, giving us problems lately running slow and crashing, trying to figure out why. I tried to do a echo 3 > /proc/sys/vm/drop_caches and that did not work. It usually puts cached to zero, did not work this time. my questions are: - what would cause echo 3 > /proc/sys/vm/drop_caches not to work? - does the *cached* value even matter? - is there another way to accurately find out current state of RAM used/cached/whatever besides the *free* command? - given this type of problem and troubleshooting, any recommendation?