Hi walspara, and welcome to AF
As Dread says, this really belongs in the Desire All Things Root forum, but I can tell you straight away what you did wrong: before running the RUU you should have flashed either the alpharev "downgrader" hboot or the "bravo stock" one ("downgrader" if you wish to remove S-Off and go completely to stock software, "bravo stock" if you wish to remain S-Off). The problem is that the "CM7 r2" hboot gives you a system partition that is too small for the stock ROM to fit, so the phone cannot boot. It has also removed your custom recovery.
If your English is limited, the simplest might be to ask your friend to change the hboot, the run the RUU again. Otherwise, here are the steps:
* You need to install "fastboot" on your computer. If you use Windows, there are instructions here: [FAQ] ADB and FASTBOOT for Windows (Updated 1st June 2011)
* Download the hboot img from alpharev.nl
* pull the battery out. Reinsert, then boot the phone while pressing the "volume down" key down. This will get you a white screen with a menu on it. Select "fastboot" on the menu and press the power key.
* when it says "fastboot" on the phone screen, connect to your computer via usb. It should now say "fastboot usb" on the screen.
* test fastboot on the computer by sending the command "fastboot devices". If it returns your phone's serial number then it's working.
* If it is, use the command "fastboot flash hboot <hboot-name>.img" to change the hboot
* then "fastboot reboot-bootloader"
* now with your new hboot, put the phone back into fastboot mode (if it isn't already) and run the RUU again. This time it should work.
As I say, your friend will have had to do this already (to install the CM7 r2 hboot), so it might be best if he can do this for you if you are new to it.
If you can't get fastboot working on your computer, you can download the hboot as a zip file from alpharev.nl. Copy this to your sd card (not in a folder, just the top of the card), rename it to PB99IMG.zip (exactly that, case-sensitive) and boot while pressing the volume down key. The bootloader will ask you whether you want to apply the update - confirm that you do. Then reboot, enter fastboot mode as described above (from the hboot menu), connect to PC and run the RUU.