You might need to use discs of higher quality.
For DVD-R discs, you should use Verbatim DVD-R (With Super AZO) discs.
For CD-ROM games, you should probably try to get some Sony CD-R discs.
Since you have a HD7 laser, your console might prefer DVD+R discs instead of DVD-R discs.
My SCPH-39006 console (With HD7 laser) can read both types of discs though.
And like Player1 has said, it might be that your modchip is starting to fail.
It might have also been your laser weakening.
Also, try updating your CD/DVD writer's firmware too.
Unmodified SCPH-77006 with SM 3.6
SCPH-39006 with M-chip modchip, SCPH-10281 NA and refurb Seagate 80GB HDD
SCPH-10000 v1.00 with SCPH-10190 PCMCIA NA and SCPH-20400 HDD unit