i have got a emachians 3210, and i have just got myself 1gb of ram too put in it. But when i put it in i get a message on screen saying check your pc and signal cable monitor is working?

Did you remove the old memory? Usually you need to go into the bios and check that the timmings are compatible and sometimes give a bump to the voltage for the RAM.

Also if you get it working, you should download the free program “memtest86+” and use that to make sure the memory doesn’t make errors. You have to make a bootable floppy or CD, the software does the work for you.