[Yum] Strange yum behavior

[Jacques]

Hi everybody
 My problem is simple, but apparently not simple to resolve.
I already asked this question on two different forums (fedora and sitepoint), without any positive answer.
Being newbie to this kind of information distribution, I apologize if any procedural order is bypassed.

 yum (and/or yumex) has lost the database of all installed packages on my FC5 system machine...
 The problem is now that :
 1- I cannot update anything, because nothing shows as installed.
 2- I cannot remove anything for the same reason.
 3- I cannot install anything because so many packages are logically not installed, making yum/yumex enter in a dependencies frenzy.
 4- beyond this problem, the machine works fine. It's still the one i'm working on at present time.
 
 Presently, yumex is configured without the Auto refresh on start in the Edit -> Preferences.
 Here is the result after going through the repositories refresh.
 
 10:03:17 : Current Settings :
 10:03:17 : autocleanup: False
 10:03:17 : autorefresh: False
 10:03:17 : debug: True
 10:03:17 : exclude: []
 10:03:17 : filelists: False
 10:03:17 : fullobsoletion: False
 10:03:17 : mirrordetection: 'best'
 10:03:17 : noplugins: False
 10:03:17 : processsafemode: True
 10:03:17 : proxy: ''
 10:03:17 : recentdays: 14
 10:03:17 : usecache: False
 10:03:17 : Mirrordetection : best
 10:03:17 : Yum Version : 2.6.1 (/usr/share/yum-cli)
 10:03:17 : Setup Yum : Config
 10:03:17 : Setup Yum : Plugins
 10:03:17 : Setup Yum : Transaction Set
 10:03:17 : Setup Yum : RPM Db.
 10:03:17 : Setup Yum : Base setup completed
 10:03:17 : Enable/Disable Repositories
 10:03:22 : Loading Repositories Data
 10:03:22 : Loading Repositories Data : Init. core repository
 10:03:22 : Loading Repositories Data : Init. extras repository
 10:03:22 : Loading Repositories Data : Init. updates repository
 10:03:22 : Loading Repositories Data : Populate Package Sack for core
 10:03:22 : Loading Repositories Data : Populate Package Sack for extras
 10:19:17 : Added 217 new packages, deleted 171 old in 24.89 seconds
 10:19:17 : Loading Repositories Data : Populate Package Sack for updates
 10:25:59 : Added 24 new packages, deleted 17 old in 5.47 seconds
 10:26:01 : Loading Repository Group Data
 10:36:47 : Loading Repositories Data completed
 10:36:47 : Building Package Lists : Updates
 10:36:50 : Building Package Lists : 0 Updates found
 10:36:50 : Building Package Lists : Installed
 10:36:50 : Building Package Lists : 0 Installed packages found
 10:36:50 : Building Package Lists : Available
 10:37:48 : Building Package Lists : 5972 Available packages found
 10:37:48 : Building Package Lists completed
 10:37:49 : Updating groups view, populate view with data 
 10:37:49 : Repository initialization completed in 2072.17 seconds
 
 Can someone give me a clue on how to rebuild the installed packages database ?
 
 I already went through a yum cleanall  and 
rm -f /var/lib/rpm/__db*  rpm --rebuilddb
It does not work either.
 
 Thanks in advance.
 Jacques