ITunes 11.0.3 asks for password again and again, have re-done my credit card details, have changed my Apple ID password, tried to log in and out of iTunes, none of thos seem to work, just keeps happening without end, please help

Question

I have tried to re-install iTunes 11.0.3 at least 6 times.
I have also downloaded iTunes 11.0.3 at least 5 times.
I have changed my Apple ID password.
I have downloaded (again, I've done that many times) iTunes 11.0.3, then I switched off the iMac, then restarted the wi-fi modem.  Switched on the iMac, loaded iTunes, same problem.
I tried to just switch off the wi-fi, did the same as point above, same problem.
Even tried to change the system date to 2038, this only seemed (although I doubt it) to fix the "not responding" issue which I had this morning.
The Apple ID password issue, where it asks me for the password loads and loads of times (probably 50 times or more), one after the other has been happening for about 3 days now.
Here is a copy of my message problem:
iTunes Problem, can't seem to find a solution online.
I am running OS X 10.8.3 on an iMac, have just loaded iTunes 11.0.3 a few days ago.
Firstly, I'd open iTunes and it would immediately say it was not responding, I'd have to force quit, try again, re-boot, try again etc.  I tried re-installing iTunes, changing password, everything to no avail, then changed my date to 2038, and voila it started responding (no, don't ask me, I just read in online and was desperate enough to try it).  Of course, I don't believe that this actually helped, I would like to know what did help or if there is something specific one needs to do to fix this.
I have not been able to get rid of this problem:  Whenever I try to make a purchase it asks for my Apple ID password, dozens of times until I give up and press cancel, cancel, cancel.
Why does it do this?  I don't want to purchase anything because I can't keep typing in my password again and again.  I'm not exaggerating.
As I mentioned, I have tried to re-install iTunes, about 6 times, and I changed my password.  I still get the same problem.
Also, my iTunes still looks like the classical iTunes and doesn't have the new interface.
Has anyone experienced this and was able to fix it, or does anyone know what the problem is?  Please help, I'm at my wits end.

Answer 1

Because too much time has passed I can't edit this into the prior comment, but here is the info regarding reverting to iTunes 11.0.2 (assuming you do have a time machine backup) from https://discussions.apple.com/message/22057703#22057703
W. Raider wrote:
Repairing permissions doesn't fix it.
I reverted to the previous version, 11.0.2.
1. Quit the new crash-prone iTunes.
2. Delete the app.
3. Restore v. 11.0.2 with Time Machine.
4. In your iTunes folder look for a folder called "Previous iTunes Libraries", find the latest one.
5. In the iTunes folder itself you'll see "iTunes Library.itl", delete it (or compress it and save a copy for later just in case.
6. Copy the newest .itl file in Previous iTunes Libraries to the iTunes folder and rename it "iTunes Library.itl".
7. Launch the older version of iTunes.
My crashing has seemed to have ceased with a revert to an older version. I noticed today that the newer crashing iTunes had been launched for hours but not playing anything, when I played internet radio it crashed within 5mins, fed up I reverted to an older version.
Btw, a simpler way to do this is to revert to older iTunes app, then hold Option when it launches and choose an older library.