To get to the root of the problem quickly, I'd try these:
With ONLY the arduino Uno connected to the computer, try to upload a simple sketch like Blink.
Check that the following are correct:
[Tools] menu > [Board] > Arduino Uno
And one more thing, try to re-install the FTDI-serial driver (you know how to do that probably)
Please report on what happens when you do that, and we can proceed from there.
Also, if the problem persists, try directly uploading using avrdude from command prompt... Not that difficult, and also useful knowledge in the future if you ever want to program small atmega chips (instead of just using the full arduino system) for your final project:
Here is a guide for that: Installing an Arduino Bootloader - SparkFun Learn