Toshiba M105-S322 Locks Up

Question

I've got a Toshiba M105-S322 laptop that freezes at random requiring a soft reboot. Sometimes it'll happen right after boot, sometimes it'll go for hours without a hitch. I'd say it's software related but I'm seeing where the system seems to have trouble consistently seeing the memory, sometimes it'll read 512MB, sometimes it'll see 1GB. I'm going to go ahead and replace the memory, but is there some way to find out if it's the MB before I do so? If it's a bad MB, I'll probably just replace the computer. Any suggestions would be appreciated.Thanks.