What programs are you trying to run simultaneously? Some programs utilize more memory or use a large cache so it may dump an unused program.
Win Media player is known to eat up RAM and may close other running programs.
Search for a program called cleanRAM 1.9.3 is latest version I think. It may help by freeing up all available ram before you start multitasking.
Here the link
http://handheld.softpedia.com/get/Sy...AM-74823.shtml