a few things I would try:
- Reset the console, listen if the disk loader resets itself. If the disk tray is empty you'll hear the drive reset.
- Make sure your inserting the disk correctly. The drive ejects disks that are upside down. I'm assuming your putting the disk face up but hey you never know! Is the disk damaged in any way? It could be rejecting the disk because it cannot be read or seat in the drive properly. Does it eject all disks or just the one disk?
- See if the eject button is stuck. Take off the front panel and re-seat the front panel just to make sure nothing is forcing the button stuck.
- Take a CO2 air can and blow out the drive. Blow out all air pathways just for good measure.
- Open up the wii and look at the drive itself. See if anything is blocking the disk from sitting within the drive correctly.
- If the Wii is new, take it back for an exchange.
My Wii (Wiikey2) sometimes acts up and wont accept disks after I'm done playing a previous game and I try to switch disks. Once I reset the console it works fine after that. If you modchipped your Wii, the wires soldered to the IC could be loose or shorting out other IC legs. I would open it up and take a look if that is the case. I hope this helps.