China DOS Union

I installed Win XP on top of the 98 system on the Lenovo computer at my company, and as a result WIN98 won't start anymore, the DOS system won't start either, and it won't even read the WIN98 boot disk now. Experts, please help me~~~~~~~~~~~~

Lenovo computer? Is it a brand-name machine?
An original Lenovo should come with a recovery CD. Just put it in, then set the BIOS to boot from CD, and it should be OK.

It seems like after changing the BIOS it changed back again, what should I do

After changing the BIOS, at the end you have to press the “F10” key to save and exit, that's the “Save & Exit” option (something like that, I think...)

That very well could be the reason!

The key is, I already chose SAVE, then restarted. The computer was a little better than before. Originally I couldn't see the DOS screen at all; after changing it, the computer screen flashed the DOS screen for a moment, then kept skipping past it. The next time it starts it's the same as before, it simply doesn't give you any time to use DOS at all. I beg you, please explain it to me again, I'm counting on you, senior.

Did you change the BIOS first boot option to CD-ROM? In “Advanced BIOS Setup” there is an option called “First Boot Device”. Press Enter on this item or use “PageDown” and “PageUp” to make a selection. Choose “CD-ROM” and then save it.
Put the Lenovo recovery CD that came with the machine into the CD-ROM drive, and it'll be OK.
If it really still doesn't work, then call Lenovo. Anyway, it's covered by a three-year joint warranty, with on-site service...

Boot with a floppy disk

Use the XP installation disc, go into Recovery Console, choose the FIXBOOT command, and give it a try!