Cyanogenmod 9 stuck in boot loop
You should be able to get into fastboot mode (which bypasses the download mode you are currently in) by pressing and holding the Volume Up and Down buttons while turning on the phone. This should get you into fastboot. From there, you can enter recovery by pressing volume up twice and power to confirm

Once you are in recovery, you will need to perform a Factory Reset/Data Wipe.

If your recovery somehow got hosed, you can download the recovery image from CM's wiki page and then get into fastboot mode and use fastboot to flash the recovery.

fastboot flash recovery "c:\location\to\recovery.img"