Sony DVD can no longer find disks?

When I place a DVD or CD in the drive, the player spins it up and then searches for the start of the disk but cannot find it. The player gives up and displays "No Disk". I have taken it apart and watched the player try to read the disk. The laser apparently tries two locations to identify the disk but fails on both. I don't see anything that could adjust the alignment, nor does anything appear to be worn out. One more note - the laser unit seems to be contacting the bottom of the disk.