Q: Uploaded system updates; now having problems playing video or games, might be missing plug-in?

That Flash Player is out of date. Please read the following bearing in mind what iMac you have (you don't state that):

You can check here what version of Flash player you actually have installed:  http://kb2.adobe.com/cps/155/tn_15507.html

You can check here:  http://www.adobe.com/products/flash/about/  to see which version you should install for your Mac and OS. Note that version 10,1,102,64 is the last version available to PPC Mac users*. The latest version, 10.2.152.25, 10.3.x beta, or later, is for Intel Macs only, as Adobe no longer support the PPC platform. Version 11.0.1.152 is for Lion.

* Unhelpfully, if you want the last version for PPC Macs, you need to go here:  http://kb2.adobe.com/cps/142/tn_14266.html  and scroll down to 'Archived Versions/Older Archives'. The first one on the list, Flash Player 10.1.102.64 is the one you download. More information here:  http://kb2.adobe.com/cps/838/cpsid_83808.html

You should first uninstall any previous version of Flash Player, using the uninstaller from here (make sure you use the correct one!):

http://kb2.adobe.com/cps/909/cpsid_90906.html

and also that you follow the instructions closely, such as closing ALL applications first before installing. You must also carry out a permission repair after installing anything from Adobe.