Playback of clips only plays between 4 and 12 frames

Question

Hi all,
I am fairly new to Premiere, have used After Effects CS4 to produce some clips, but need something that handles editing better, and I thought I would give Premiere CS4 a try.
Unfortunately, I can't get Source or Sequence preview working.  I click the play button and the video plays for about 1/2 to 1/4 or a second (between 4 and 16 frames) and then stops, returning to the place where I hit play.  Almost like I had selected an in and out of 14 frames and hit "play in to out".
The duration of the playback is random, but never more than a full second.
The computer I am on is:
  Model Name: MacBook Pro
  OS: Snow Leopard 10.6.2
  Processor Name: Intel Core 2 Duo
  Processor Speed: 2.4 GHz
  L2 Cache: 3 MB
  Memory: 4 GB
  Bus Speed: 800 MHz
  Chipset Model: GeForce 8600M GT   
  Bus: PCIe
  VRAM (Total): 256 MB
  Vendor: NVIDIA (0x10de)
  RAM Size: 4 GB
  Type: DDR2 SDRAM 667 MHz
  HDD: 500Gb 7200RPM (50% empty)
Apple system updater says I am up to date.
I have Adobe Premiere CS4 installed (trial) 4.2.1 (003 (MC: 166418))
Adobe Updater says I am up to date.
I have done the following to try and resolve:
* Tried different source files (mp4, mov)
* Tried rendering a video in After Effects CS4 as MOV H264 and importing
* Tried putting still frames on the time line and playing those (no effects, no transitions)
* Tried playing no video, just music
* Ensure that "clear all markers" is done on the source and preview monitors
* Ensure loop is not playing
* Force in and out markers to a 5 second clip and press play
* Full deinstall and reinstall of all adobe products (I had some CS3 left overs that I cleaned out)
* Deleted all adobe application preferences folders before reinstall
* Deleted plugin cache
* Created new projects and tried all the above.
I have tried shutting down every other program before running Premiere, it is definitely not a resources problem, there is 3Gb of RAM free and CPUs sitting at 5% when I try this.
I am looking at buying Premiere, but if I can't get playback to work it's a bit of a waste
Anyway, any help or pointers would be appreciated!
Mikel

Answer 1

Thanks everyone for the long thread and lots of comments, unfortunately I have tried them all.
I even purchased a full copy of Premiere Pro (as part of a Masters collection set) and this still has not fixed the problem.
The screen recording of my problem is exactly the same as the one linked to here: Screen Recording 2 720p.mov, and I am also going to open a support ticket with Adobe.
Another point is that it even does not work on a tiny video that I used (320 x 240px)  Still same problems.
This is very frustrating.
It should be noted that After Effects and Encore both play videos fine in a similar situation, it is just Premiere that is bombing out.
See the first post for my configuration, it is still the same, except now I own a full copy of Premiere Pro as part of CS4 Masters collection.
Any further ideas?
Mikel