The device is initialized and the clear and present functions work and I also call Begin and End before and after the the renderTriangle function. I suspect I've missed something obvious but I can't come up with what that would be. I've initialized the vertexbuffer and filled it with the data for a single triangle, set the FVF, matrices (I've tried both having the camera at 0,0,-10 and 0,0,10 because I got tired and didn't bother thinking about from which way I should see the triangle because of culling) and I render it but nothing shows on screen.
public void initializeTriangle()
{
testVertices = new float[9];
vb = new VertexBuffer(device, sizeof(float) * 9, Usage.WriteOnly, VertexFormat.Position, Pool.Managed);

testVertices[0] = 1.0f;
testVertices[1] = testVertices[2] = 0.0f;
testVertices[3] = -1.0f;
testVertices[4] = testVertices[5] = 0.0f;
testVertices[6] = testVertices[8] = 0.0f;
testVertices[7] = 1.0f;

Matrix view = Matrix.LookAtLH(new Vector3(0.0f, 0.0f, 10.0f), new Vector3(0.0f, 0.0f, 0.0f), new Vector3(0.0f, 1.0f, 0.0f));
Matrix projection = Matrix.PerspectiveFovLH(2.0f, 1.0f, 1.0f, 100.0f);
Matrix world = Matrix.Identity;

device.SetTransform(TransformState.Projection, projection);
device.SetTransform(TransformState.View, view);
device.SetTransform(TransformState.World, world);

device.VertexFormat = VertexFormat.Position;

DataStream stream = vb.Lock(0, 0, LockFlags.Discard);
for(int i = 0; i < 9; ++i)
stream.Write(BitConverter.GetBytes(testVertices), 0, sizeof(float));
vb.Unlock(); }

public void renderTriangle()
{
Result res = device.SetStreamSource(0, vb, 0, sizeof(float) * 3);
res = device.DrawPrimitives(PrimitiveType.TriangleList, 0, 1);
}

If you installed the DirectX SDK (which I'm assuming you did), use PIX to debug your application.

You will be able to find the bug easily once you get a little used to PIX.

I used PIX to see the information, and the pictures of the triangle I try to render and it looks just as I expected and right in the viewport etc. I see this in the Pre-VS, Post-VS and Viewport images in PIX but what I don't understand is how nothing still isn't showed on the screen/buffer. I thought the color of the triangle is the same as the backbuffer clear color, but I changed the material in SlimDX and set ambient to white and backbuffer clear color to black (and also tried a lot other colors) but no luck. I also took a look at the depthbuffer but nothing is there.

This is confusing to me. I'm all lost right now, any help would be GREATLY appreciated, thanks!