Changes? Did it ever work? Is the internal modem new and you need a new port?
Get someone at the keyboard that will patiently follow directions and read the screen to you. (I refuse to support my brother cause I'll hear typing and he'll say "I'm trying something". Done - call me back when your done tryin' stuff!) Always helps if you follow along on your computer.
Ideas:
COM ports are typically serial ports, modems, IRDA connections etc. You get 4 ports only. Remember what you do (so you can put it back if needed).
BTW old modem cards may not be selectable in software may require jumper or dip switch change on card. Also you may need to change the IRQ also (these are limited also). Newer computers and OS's scale better with all the crap we hang on 'em.
Option 1
Note my version of Windows differs. In "Device Manager" check out "Ports (COM and LPT)", "Communications ports", "Port Settings", "Advanced" - COM Port setting should list current port for chosen device and all ports used. Are all 4 used? You can manually rearrange ports - perhaps multiple ports want port 4 as a default.
Option 2
Your machine may have a serial port unused in back (or your mouse may be connected to it).
If you have an empty serial port in back (usually a 9pin plug like a small parallel printer plug) it is likely using a com port set in the BIOS.
BIOS - You know when you boot and it says something like "F1 for Setup", this is the hardware boot defaults in your machine. Tells the machine how to use the harddrive etc. before the OS loads. Remember you must save the settings.
Check it out, quickly on boot hit whatever key it says gets you to setup. Remember you don't have an OS yet so no mouse - follow lousy instructions - they are all different. Disable the serial port (usually something like Com port 1, Com port 2, disable).
Boot Windows see if it rearranges properly or you can rearrange the ports manually.
OPtion 3
If you have an option "PnP OS" (plug and play OS) select it. This will give WIN98 control over all devices. This will likely cause WIN98 to redo all its device ports because it can rearrange things that were set by the BIOS.
Best Option
Just a plug for Dell... Dimension 2400 $299 (with $75 rebate that you really get) plus shipping. Complete system modern, entry level for today - a dozen times bigger and faster than your 200! Unpack and it works! Decide how much hassle the old 200 is worth!
Luck!