Used this Apex Ad-2600 DVD player only a few times. Has been
sitting in a box for close to 10 years. Tried it out the other day,
and every type of disc loaded gives the same 'no disc' message.

A couple of thoughts:

- It might be worth checking the power supply. I think that player
was made during the era of the "stolen-electrolyte bad capacitor
plague" problem. It's possible that the power-supply bypass
electrolytic caps have gone bad (they usually fail as a result of
power-on hours, but I suspect they could have gone bad in storage
as well). Signs and symptons might be swollen tops on the
capacitors, obvious signs of leakage of electrolyte, or (if there's
no external failure) excessively high "equivalent series
resistance" or excessive noise and ripple on the power supply
rails.

The cure would be to remove any such suspect capacitors, repair any
damage to the PC-board traces caused by leaking electrolyte, and
replace them with high-quality low-impedance/high-frequency-rated
"switching supply rated" electrolytics (Panasonic and Nichicon are
good brands).

I had a Cyberhome DVD player of about the same vintage which failed
due to this problem. Replacing the caps fixed it.

- It's possible that the "sled" which moves the optical assembly back
and forth is stuck in place. Whatever lubricant was used on the
sled "rails" may have congealed over the years. Fixing this would
require opening up the drive (if it's sealed), gently sliding the
sled back and forth by hand, cleaning the old lubricant or grease
off of the rails (Q-tip or chamois swab, plus 99% isopropyl alcohol
would probably do) and then lightly re-lubricating the rails
(Tri-Flo, or sewing machine oil - don't use WD-40).