I'm usually pretty handy but I gave up trying to fix this problem. However, I loved the cartridge cart on the 7510 (so easy to remove and clean) so I looked for other HP printers that used the same cartridges. Walmart had a sale on refurbished HP 5520. They were practically giving it away for around $50. Heck, the new cartridges alone were worth 20 to $25. I bought refillable cartridges and it has been running beautifully for the past 6 months.

Figured it out!! Reach into the paper feed area from the front. Feel for the pick-up roller assembly (it has two rubber rollers on it). There is a small plastic piece on the bottom of the roller assembly that slides to the right (when facing the front). After sliding that piece to the right, the pick-up rollers are working fine again !!