hi
well telling us which os you are using will help to determine if you have enough memory.reading from your post i asume that youy had 64 before somone has upgrade it and put another 256.
running a few aplication at once (specially graphic ones) requires little bit more memory.
what is your cpu?more details you provide to us will help all of us to get proper answers.
you sadi you have a share of problams...ok what are they?whats happenign?does pc freeze or reboots or whats happening???
pls provide us with little bit more details
in a mean time have a look this site to give you an idea
http://www.computermemoryupgrade.net...er-memory.html