The latest update for PrPro CS5 is 5.0.3.
If you couldn't download 5.5.2 update, which is for CS5.5, it hardly had a chance to interfere.
If you managed to download it and then attempted to install... I don't know...
If you have the latest driver updates installed for your GeForce GTX 470 as well and still can't playback the timeline even with offline media (try Craig's suggestion about 'Bars and Tone' to see if it makes any difference, BTW), I'm almost run out of idea...
As just a ritual dance, try to
1. Clean up your Media Cache Database. Navigate to
C:\Users\Ernie\AppData\Roaming\Adobe\Common\Media Cache and
C:\Users\Ernie\AppData\Roaming\Adobe\Common\Media Cache Files and manually delete all files in both folders.
2. Deactivate and then reactivate PrPro
If nothing else helps, and some other worthies won't be able to give better advice, create backup copies of all files in Adobe directories you want to store, uninstall PrPro, probably, run Adobe CS Cleaner Tool and then reinstall PrPro...