DVDs Skip

I built my computer in January 2007. For many many months, my DVDs played just fine on my computer. (I had my Plextor in my last computer and DVDs played just fine as well.)

(By skipping I mean that both the video and the sound aren't fluid. The skipping is throughout the entire movie and on all DVDs that are played.)

Around the July time frame, my DVDs started skipping. In June, I installed Adobe Premiere Elements video editing software.

I reformatted my computer and the DVD skipping problem went away. Well, I recently installed the Adobe software and then about a month later, the DVDs started skipping again.

Interestingly, the DVDs will play fine (most of the time) when I'm logged on as administrator. When I'm logged on to a Limited account, the DVDs always seem to skip. But, if I run the DVD player software as administrator within a Limited account, the DVDS didn't skip.

I've also run trial versions of WinDVD and PowerDVD and the problem still exists. I also installed the trial of nVidia's DVD player codecs. The DVDs still skipped.

I also changed the sound card to no avail.

Do you think it's a codec conflict of some kind?

Any suggestions?

Thanks in advance.

Configuration:
DVD ROM: Plextor 708A
Motherboard: Intel D965RY
Processor: Dual Core 1.86
Graphics Card: nVidia 7600GT
RAM: 4 GM
OS: XP Pro
Hard Drives: 1 Serial ATA @ 300 GB, 1 IDE @ 320GB (both Western Digital)