HL-DT-ST DVDRAM GSA-T20N ATA Device gone!!

   I have a Compaq Presario 700 series notebook.  A few days ago I tried to play a DVD, which I have had no problems in the past doing, and it wouldn't work.  Tried several more and they didn't work either.  I even had problems getting the drive to open up.  Went into my device manager and there is no dvd drive listed....it has disappeared!!  I haven't done anything new to my computer recently to explain it, either.  Anyway, I found a solution here to try going into regedit and modifying the upper and lower filters, but I don't have numerical values listed to modify, this is what my registry says: 
Lower filters    REG_MULTI_SZ    PxHelp20

Upper filters    REG_MULTI_SZ    GEARAspiWDM

Help!!  What do I do now??
Thank you!!

I'm sorry, but do not know what you mean by "delete key".  Just delete everything in both of the fields?


Lower filters    REG_MULTI_SZ    PxHelp20
Upper filters    REG_MULTI_SZ    GEARAspiWDM

Make it look like this:

Lower filters
Upper filters

or do I just delete the PxHelp20 and GEARAspiWDM?

When I do this, will I lose the functionality of the burner or any other functions?

Thanks, I have just never had this happen before, and it is so frustrating!!
Marie