Duffy, thanks for your advice, unfortunately it doesn't seem possible to edit the header, I could edit the rest but, I don't know what's in it anyway. I know there's a graphics card in, don't know what type but, I don't think that's the problem. There's no modem or sound card in there so, it can't be that either.
As far as I know, there's only a hard drive, floppy drive & cd rom. I've tried disconnecting all of them except hard drive but, still get the same thing when I power it up.
I hope this additional information is useful.