To begin with, you could try manually searching for COMMAND.COM
It should be on your C: drive, but you may have to make it visible by opening up your Control Panel, click on Folder Options, select the option to Show hidden files and folders and click Apply then OK.
Assuming your computer is starting properly, COMMAND.COM should be there because there is a line in AUTOEXEC.BAT ("COMSPEC=C:\PATH") that goes looking for it when you computer loads up, assuming in this example that your COMMAND.COM is on C:
To begin with, before you do anything else, I'd click Start, click Run the type the following:
then click OK.
Insert your Windows CD and scan for any altered, changed or otherwise missing or molested files. There's a nice tutorial on System File Checker at this link click here
I don't think you can rule out a hardware fault with your keyboard, but try running SFC before you do anything else and see what comes up.