What does "Non-system disk or disk error. Replace and strike any key when ready..." mean?
This error message usually means that you started your computer with a floppy disk still in the 3 1/2" Floppy Disk Drive. The computer is telling you that there are no Windows 98/ME/XP system files on the floppy disk, so it can't start up on the disk.
To resolve this problem, push the Eject button on the front of the 3 1/2" Floppy Disk Drive (the part with the slot that's about 3/8" high and 3 1/2" wide which is covered by a little door when there's no floppy disk in it). This will eject the floppy disk. Then push any key on the keyboard, and the computer should start up on the hard disk instead of trying to start up on the floppy disk.
If this fails to correct the problem, then you could have a bad hard disk in your computer, and it may be time to call your computer consultant.