Yes, that is the poly fuse.

It suggests that either there is a fault on your board or your multimeter drives a different amount of current than mine.  Since there are active components on the board, it is a fuzzy test.

Going back to your previous question, you should only apply 5V to the 5V pin, if you have a power supply that can limit the current.  On the other hand, if you don't apply current limiting you are very likely to find the source of the problem. 

Do you have access to a high-resolution scanner?   It might worth while to post good pictures of the top and bottom of the board. 

Would love to help.

General Electronics
Science and Measurement
Other Hardware Development

Anyone on how to work around the powerpart of the Arduino. Shall I try and put 5v on the 5v Pin, or do i make things worse. Well It can´t get any worse then this.....

Take two resistance measurements with your multimeter on your un-powered Uno:

1.  Measure between the 5V and GND pins?  (I am seeing about 940ohms)
2.  Measure across the poly fuse, the component between the USB jack and regulator.  (I measure 1ohm)

You might be interested in this excellent analysis done by westfw:

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1283329855

Is there a question in your post?

Doesn't that just hold the CPU at 100% usage and make it waste battery power?

As others have noted, microcontrollers just run in a loop.  In fact, unless you explicitly tell them to go to sleep, they just keep doing whatever you tell them to do.

The reason I am posting is because you have made an assumption in your statement which may not hold true for code you are looking at.  The comment "waste battery power."   That is an assumption, which can be dangerous.

Just because you might intend to use battery power in your application, do not assume that code you are looking at from others are going to as well.  (Obviously, this applies to more than just while(1); loops.)

I'm surprised the computer is not complaining about your board drawing too much current

Maybe the Arduino's poly fuse is not opening completely and is dropping most of the voltage.  It would keep the current draw from the PC down and would explain the low on-board voltages.  Do you have another PC or a USB Hub you can attach the Arduino to?  (To verify the USB port you are using can actually deliver a load.)

If nothing else is connected to the Arduino, a visual inspection of the board is in order.

Knowing this piece of information, I would NOT take my previous advice and connect your 12V 2A supply.  If there is a short, you may permanently damage the Arduino.

The Arduino's on-board regulator can actually handle up to 20V.  12V is actually recommended because of the additional heat generated above 12V.

Most Wall-Warts only produce the rated voltage under load. 

As a very quick test, you can safely attach your wall wart to your Arduino and measure the voltage at Vin or directly on the barrel jack.   If the small load of the Uno is enough to put the wall-wart into regulation, you will be fine to use it.  If this test still shows >12V, do not continue using this power supply with the Arduino (unless you apply a larger continuous load in addition to the Arduino.)

Again, because the Arduino's input regulator can tolerate >12V and if there is no other load, briefly applying 17V to the input should not be damaging.  You should not run the Arduino long-term with an input higher than 12V.

With the USB cable powering the board, what should the voltage be at the 3,3v and 5v pins?

The 3V3 pin will be very close to 3.3V.  The 5V pins will be whatever the Vusb of your PC is at the time.  The USB spec allows this to be in the range of about 4.7v-5.2v (maybe a little wider than that.)

Add a very large delay immediately after changing your reference, but before the next analogRead.

I vaguely recall problems occurring if you do an analogRead() too soon after changing the reference.

When I say large, I mean a couple hundred (to 1000) milliseconds, at least as a trouble shoooting step.

No, the barrel jack and the Vin pin are the same node.

As stated, USB is technically a regulated voltage.

Aside from that, you generally cannot take an input voltage, regulate it, and achieve the same output voltage.  Some voltage drop must be accounted for by the regulator.

The term "Ground" is something we all made up to refer to the reference plane.  Remember that voltage is relative to some reference.  In this case that reference is 0V.

So all supplies and components need to share a common Ground to work (except in the case of isolators, of course.)

Your posts are a little bit of a contradiction.  The first post you say you want a connection such as PC to Arduino to Xbox.  The next post you say you want a device that lets you connect your keyboard and mouse to the Xbox.

If the 2nd is what you really want, then the Arduino is not an ideal solution.  It would need to act as a USB Host and USB device.  That's a pretty significant amount coding of effort.  You could be better off hacking a Xbox controller.  Determine all of the button and knob connections, then connect those to an Arduino.  This is also a significant amount of effort.

The ISP programs the microcontroller's on-board flash ROM.  To make sure the processor is doing nothing while this occurs, the processor must be held in Reset.

I capitalized the word for emphasis.  I assume from your first post you are familiar with the concept of resetting a microcontroller.