Also die neu angelegte Mediathek hat nix geändert (Wie komme ich denn jetzt wieder an meine alte Mediathek?).
Etrecheck hat dies hier ausgespuckt:
Problem description:
iTunes
EtreCheck version: 2.1.1 (104)
Report generated 8. Dezember 2014 18:00:00 MEZ
Hardware Information:

iMac (21.5-inch, Late 2009) (Verified)
iMac - model: iMac10,1
1 3.06 GHz Intel Core 2 Duo CPU: 2-core
4 GB RAM Upgradeable
BANK 0/DIMM0
empty empty empty empty
BANK 1/DIMM0
empty empty empty empty
BANK 0/DIMM1
2 GB DDR3 1067 MHz ok
BANK 1/DIMM1
2 GB DDR3 1067 MHz ok
Bluetooth: Old - Handoff/Airdrop2 not supported
Wireless: en1: 802.11 a/b/g/n
Video Information:

ATI Radeon HD 4670 - VRAM: 256 MB
iMac 1920 x 1080
System Software:

OS X 10.10.1 (14B25) - Uptime: 0:5:9
Disk Information:

Hitachi HDE721010SLA330 disk0 : (1 TB)
S.M.A.R.T. Status: Verified
EFI (disk0s1) <not mounted> : 210 MB
Macintosh HD (disk0s2) / : 999.35 GB (833.71 GB free)
Recovery HD (disk0s3) <not mounted> [Recovery]: 650 MB
HL-DT-ST DVDRW GA11N
USB Information:

Apple, Inc. Keyboard Hub
Apple Inc. iPhone
Apple, Inc Apple Keyboard
Apple Inc. Built-in iSight
Apple Internal Memory Card Reader
Apple Computer, Inc. IR Receiver
Logitech USB Laser Mouse
Apple Inc. BRCM2046 Hub
Apple Inc. Bluetooth USB Host Controller
Gatekeeper:

Mac App Store and identified developers
Problem System Launch Agents:

[failed] com.apple.syncservices.SyncServer.plist [Details]
Launch Agents:

[loaded] com.oracle.java.Java-Updater.plist [Support]
[running] com.teamviewer.teamviewer.plist [Support]
[running] com.teamviewer.teamviewer_desktop.plist [Support]
Launch Daemons:

[loaded] com.adobe.fpsaud.plist [Support]
[loaded] com.oracle.java.Helper-Tool.plist [Support]
[loaded] com.teamviewer.Helper.plist [Support]
[running] com.teamviewer.teamviewer_service.plist [Support]
User Launch Agents:

[loaded] com.adobe.ARM.[...].plist [Support]
User Login Items:

iTunesHelper Programm (/Applications/iTunes.app/Contents/MacOS/iTunesHelper.app)
AdobeResourceSynchronizer ProgrammHidden (/Applications/Adobe Reader.app/Contents/Support/AdobeResourceSynchronizer.app)
SpeechSynthesisServer Programm (/System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/SpeechSynthesis.framework/Versions/A/SpeechSynthesisServer.app)
Internet Plug-ins:

FlashPlayer-10.6: Version: 15.0.0.239 - SDK 10.6 [Support]
Default Browser: Version: 600 - SDK 10.10
AdobePDFViewerNPAPI: Version: 11.0.09 - SDK 10.6 [Support]
AdobePDFViewer: Version: 11.0.09 - SDK 10.6 [Support]
Flash Player: Version: 15.0.0.239 - SDK 10.6 [Support]
QuickTime Plugin: Version: 7.7.3
OfficeLiveBrowserPlugin: Version: 12.3.6 [Support]
JavaAppletPlugin: Version: Java 7 Update 67 Check version
Safari Extensions:

Extensions: No such file or directory
3rd Party Preference Panes:

Flash Player [Support]
Java [Support]
Time Machine:

Time Machine not configured!
Top Processes by CPU:

7% WindowServer
6% firefox
2% plugin-container
0% AppleSpell
0% fontd
Top Processes by Memory:

331 MB firefox
202 MB plugin-container
155 MB Finder
112 MB iTunes
94 MB mds_stores
Virtual Memory Information:

983 MB Free RAM
1.98 GB Active RAM
795 MB Inactive RAM
538 MB Wired RAM
1.34 GB Page-ins
0 B Page-outs
Diagnostics Information:

Dec 8, 2014, 05:55:33 PM Self test - passed
Dec 8, 2014, 03:10:37 PM firefox_2014-12-08-151037_Axels-iMac-3.cpu_resource.diag [Details]
Dec 7, 2014, 02:15:56 PM iTunes_2014-12-07-141556_Axels-iMac-3.hang
Dec 7, 2014, 02:03:26 PM iTunes_2014-12-07-140326_Axels-iMac-3.hang
Dec 7, 2014, 01:58:29 PM iTunes_2014-12-07-135829_Axels-iMac-3.hang
Dec 7, 2014, 01:55:31 PM iTunes_2014-12-07-135531_Axels-iMac-3.hang
Dec 7, 2014, 01:54:46 PM iTunes_2014-12-07-135446_Axels-iMac-3.hang
Dec 7, 2014, 01:48:17 PM iTunes_2014-12-07-134817_Axels-iMac-3.hang
Dec 7, 2014, 01:43:38 PM iTunes_2014-12-07-134338_Axels-iMac-3.hang