The BIOS is looking for the files needed that start to load Windows, in this case it is the file Command.com. Try This: (the latter Worked for me, about 5 years ago)
Throw away your windows 98 Setup Disc. Go to your local retailer and purchase Windows XP with SP2, its well worth it. If this is not an option try this:
Insert a Windows startup diskette into the A drive. If you do not have an A drive you will need to have a bootable CD with the required files. If you made a startup diskette from the same operating system (version of Windows) and you have Sys.com on the diskette or can copy it from the Windows\Command folder to the diskette; at the A:> prompty type Sys C: and sys.com will transfer the required bootup files. Dont forget to change the boot priority in BIOS to suit.
If you do not have the Sys.com or not the correct startup diskette then type the path to Command.com: A:\Command.com and press Enter. You now have MSDOS running, and hopefully you have Scandisk.exe on your startup diskette. Next, type the word Scandisk.exe and press Enter again. Have Scandisk check and repair your C drive for errors. If Scandisk is not on your floppy, you can find it in the Windows\Command folder
Then copy Command.com from our startup floppy to the C drive.
Type: Copy A:\Command.com C:\Command.com and then press Enter. You probably should also copy the IO.sys file on your floppy to C drive, just to ensure that it's there. DO NOT copy the MSDOS.sys file. By the way, the file IO.sys is probably going to be a hidden file so you will need to remove the Attributes. They should be Hidden, System, and Read Only. So you will need to type at the A prompt "Attrib -H -S -R IO.sys" and then press Enter before copying the file.
Now reboot, hopefully you will not get the error message again. If you do get the message again, you may need to have Fdisk fix the Master Boot Record: from your Windows\Command prompt, type : Fdisk /mbr and then press Enter. This only takes less than a second and no message will be displayed.