The Invalid function message

[Geek-9pm]

Go ahead. Have fun. Be aware that many people have had trouble with CD and DVD players but the fault was not always the hardware.
My point was that it is much harder to get information about why a hardware devcie does not work in MS-DOS. This is because the hardware was made after support for the OS had passed.  Newer CD drives  have some parameters that differ from the early designs. Nd not just CD /DVD readers. All new hardware has the potential to be incompatible with any older OS.

I did a quick look   on Google for the kind of issue you have and found there are many reports even Window XP had trouble with some makes of CD/DVD drives. The response fro some became a very long discussion about the how to replace or fix  the drivers,  but missing from the tutorials was the specific information about the parameters needed by some CD/DVD drives. Microsft has more about this.

Of the hundreds of things I found, here is one MS  worth reading:

DVD Drive Repair

DVD Drive Repair is a useful application that allows you to restore your DVD (Optical) Drive if missing from Windows. In some instances, it can also help when certain applications do not recognize your drive; mostly when your computer encountered a hardware problem or a virus attack that prevents it from using the DVD Drive.

However, this tool is not for MS-DOS. 

Moral: use only old hardware with old OS.   

[patio]

See here...

The 1 i had best success with back when was the OakRom driver...

[BC_Programmer]

It's worth noting that CD1.sys is a (relatively) recent Driver. There is also a consideration here in that it attempts to use UDMA, given that UDMA generally involves Upper Memory it could at least make sense of the behaviour being seen. I believe it is designed primarily for things like freeDOS running on relatively recent systems, rather than "original hardware/software" systems which often had flakey bus-mastering featuresets, if they had them at all.

OAKCDROM.SYS referenced above is my own go-to for MS-DOS systems to enable Optical drive support. it does not attempt to use UDMA and uses Programmed I/O which makes it more compatible.

[patio]

the directory you install the driver to needs to be added to the Path also...

[Lisa_maree]

Thank you for the info about no adapters and the DVD is IDE.

You could try doing this and it might show what isn't loading properly
Quote from http://smallvoid.com/article/bypass-step-through-config-sys.html

MS DOS 6.0 introduced the ability to bypass the Config.sys and Autoexec.bat, and only load the Himem.sys, or single step through the Config.sys and Autoexec.bat. This can be useful if having problems with diagnosing what device driver or other terminate and stay resident (TSR) that is causing problems.

These options can be activated by pressing the keyboard key F8 during startup, when it displays "Starting MS-DOS ..." (Shown for two seconds). If pressing F5 instead of F8 then it will bypass the startup files without showing any options. MS DOS 7.1 (Win98) also reacts to CTRL being held down (same as F8), instead of waiting for the right moment to press F5 or F8.

It would help if you could give some details of the computer
Motherboard and total memory, graphics card any other cards you have in the computer.

Thanks

[Geek-9pm]

To make this thread more useful, here are links to CH articles about a "DOS 7" download and related stuff.

https://www.computerhope.com/forum/index.php?topic=129598.30

https://www.computerhope.com/shutdown.htm

https://www.computerhope.com/edithlp.htm

Below is about Free DOS.
https://www.computerhope.com/forum/index.php?topic=73359.0

[infiniteness84]

So after being sick for quite a long time I decided to reinstall DOS once again. The result is that now everything works and I have no idea what I did different this time.

[Geek-9pm]

So after being sick for quite a long time I decided to reinstall DOS once again. The result is that now everything works and I have no idea what I did different this time.

I know the feeling.