Create a new document (Ctr+N), 400 pixels x 400 pixels with RGB colour and white background. Create a New Layer (Ctrl+Shift+N) and call it Back. Press “D” to return the colours to their defaults (Black and White). Then go on Filter -> Render -> Clouds.
To create the rather abstract effect, do a Filter -> Distort -> Wave. Choose the following options:
Number of Generators: 2
Wavelength: Min – 122
Max – 178
Amplitude: Min – 29
Max – 999
Scale: Horizontal – 100%
Vertical – 100%
Make sure the Type is set on Square as this is the main feature, set the undefined areas as “Wrap Around” and click Randomize until you are happy. Try to make it more squarish and even
You should get something like this:

Then having done this, go to Filter -> Distort -> Shear. Do something very random and wavy according to choice. Select “Wrap Around” and click “Ok”. Again do a Filter -> Distort -> Wave and keep exactly the same settings but click randomize a few times to get a more random effect than last time. You should get something like this:

Repeat the last two steps as many times as you want trying not to get too off course, but keeping it random and offline.

Then to colour it – Go to the Hue and Saturation menu (Ctrl+U) of that layer and select colourize.
I chose blue in this tutorial, but you can do whatever you want. So put the following into the menu:
Hue: 250
Saturation: 75
Brightness: 9 (this depends on which colour you pick. Try to pick out the outlines so don’t make it too dark)
I am now here:

Now to create a border. Create a new layer (Ctrl+Shift+N) and call it “Blank”. Then take the fill tool (G) and press X which should select the white background colour and switch it to foreground. Fill the whole are with the paint bucket and change the layer opacity to 50%. Then select the eraser tool (E) and change the mode to Block. Zoom in a couple of bits to 400%.
Using the block eraser, go around the top edge of the Blank layer deleting around the background. So basically erase all that that you want. To do this, press Shift and drag horizontal on the top left hand block erasing all the white from this. Keep going along all the blocks trying to keep the line random:

Do this along all the sides and the bottom to create a border of the abstract background.
The sides are difficult because usually they correlate to well and there are no vertical lines other than one, so just make it up, but make sure that all the lines are straight (use the Shift key). It should end up like this:

Duplicate the background layer and call it Back_2. Create a new layer in between the two backgrounds and call it Shading. Then select all the white area by Ctrl+Clicking the “Blank” layer, go to the bottom Back layer and press Delete, which will form a border around the edge. Then go on Select -> Modify -> Expand and if using my image size, put in 5 and click Ok. Select the top Back layer and click delete. De-select the Marquee – Select -> Deselect (Ctrl+D). Then make the top Blank layer invisible by clicking the eye on the layers pallette. You should now have 5 layers:
Blank (the white area above your border - invisible)
Back_2 (the second, thinner border)
Shading (blank layer)
Back (thick border)
Background (background – white)
Select the third layer (Shading), set its’ blending mode to overlay and using the pencil tool at 16 pixels, go around the bottom and right edge of the border in white. This should create a thin (5 pixel thick) edge on the Border. Then do the top and left edges in black. You should now have a nice "3D" effect around the border. If you wish you can put an image inbetween the background and the border: