cant boot up my computer

my computer starts up and gives an error message: Invalid system disk
Replace the disk, and then press any key.
i cannot get a windows 98 boot disk to work, which is what the computer has, but i can get a windows ME boot disk to work. the message :Type the name of the Command Interpreter (e.g., C:WINDOW\COMMAND.COM) comes up, but no command i enter works. i also cannot get my windows 98 cd to boot on startup, it says failure. i can get a windows ME cd to work though, it goes through all of the pre instalation stuff, but when it comes time to copy files, it wont let me, probably because the ME cd is made for a dell. i have no clue what else to try. thanks for any suggestions u might have.