Most likely causes:
Sequence settings do not match the source media
Under powered System
Have conflicting codecs installed
Welcome to the forum.
I will take Curt's #1 suggestion - the Assets do not match the Sequence Preset.
Now, when you drag the AVI to the Timeline, what color is the line above that Clip, red, yellow, or none?
If red, or yellow, when you hit Enter, does it turn green, and now playback?
Also remember that the Source Monitor (the playback from the Project Panel) is just a playback device. When you drag to the Timeline, things change. Now, you are talking about a Clip that you are going to edit - not just playback.
There are some other things that we can check, but let's get past these first, before we move on.
We are using AVI footage that was captured using an AJA LE board and have been put onto external HDs. I have downloaded the drivers for that board. I have copied and pasted the the clips onto the internal HD, which is striped Raid 0. It was done by Dell, when my client bought the computer. Dell also made it the C: drive with the OS and all programs on it.
I will check the assets and sequence presets to make sure they are the same, but I think they are. I am not in front of the computer at the moment.
When I drag the clip into the time line there is no color on the above the clip. When I hit the space bar to play back the clip the curser or scrubber jumps back to the head of the clip and does not move. This happens no mater where in the clip I park the scrubber.
I am getting my client to email me the specs on the computer too.
I use a very old version on XP pro it is 2.0, but it very stable. I do not do heavy editing on it, just cutting up avi and wmv files to put on the Internet and some other small things. I use FCP for all of my main editing. so Premiere is a learning process for me.My client bought it to work on some of his show video, from MMA shows, to rough cut some promos and cut up the shows to put on the Internet for on demand ppv. He owns the UWC MMA shows. He wanted to learn editing and one of the other editors use premiere so all the footage is from his editing.