a few things you can try:
1. type top (this will tell you how much ram you have and how mush is used
2.
http://www.memtest86.com/ (ram test program
3. if your ram amount is wrong then:
Follow the next steps to modify /etc/lilo.conf and add this line:
Using your favorite text editor modify /etc/lilo.conf and add this line:
append = "mem=512M"
then save and exit and run /sbin/lilo to save changes on boot
Reboot and check it out typing: top or free
If you are using loadlin add the parameter: mem=128M on its command line