I appreciate that it's not in the subject, but still, you should not tag your posts as urgent. Those who are uninterested in your problem are not going to be swayed by assertions of urgency; some of those who otherwise would help will take offense at it (myself included). Remember that each of us could be out talking to girls (or boys), but have instead chosen to come volunteer time here.
I think you're saying you enabled repos for two different versions of Debian? Honestly, if you're a newbie and don't have too much invested in that system, my guess is the damage is so widespread that it'd take you twenty times longer to fix enough that you're functioning again than it would to just nuke it and reinstall. Before you do so, get a largeish USB-able storage device and:
cp -ar ~/* /media/yourdisk
cp -ar ~/.* /media/yourdisk
The latter version is to catch hidden files, which your shell will probably not include in ~/*. Afterwards, you can reverse the arguments to copy everything back to your homedir on a new system. Don't forget the hidden files! You may also want to get /etc for system and various programs' configs. (And obviously, substitude for /media/yourdisk as needed. No reason you can't make a directory specifically to put this stuff in. Don't just do; understand.)