gdgt

I'm getting various video playback problems on my Nokia 5800:

Screen goes black and I have to use slider switch to reactivate
Screen gets a coloured hue (red, yellow, purple or blue intermittant) while watching and video, just wait and it goes back to normal after a few seconds.
If I jump to another section of the video the phone takes a long time (several minutes) to continue playing and sometimes never continues.
If I pause the video and then continue after doing something else with the phone, I get horizontal lines on the screen for several seconds, sometimes minutes.

I've had these problems since I bought the phone last January and Carphone Warehouse said to upgrade the software. I upgraded to V 21.0.025 but the phone still has these problems.

I know there is another newer version of the software and I plan to try that over the next few days.

Is this a known problem?
Does the new software cure it?
Should I just get the phone replaced / repaired?