I have rewritten the MBR with the MiniTool Partition Wizard Bootable CD 7.0 and booting works fine now.
http://www.partitionwizard.com/partition-wizard-bootable-cd.html

Once again, thank you for your help!

I can now access it from my friends computer while being in the external HDD caddy but will it boot when I put it back into my old computer?

Thank you for your help so far!

I defragmented it. Sorry!

I can see the volume but I get an error message when I try to access it (click link for picture).

http://imageshack.us/photo/my-images/585/computerh.jpg/

I ran MyDefrag with admin rights and before the defragmentation no access restrictions applied to the partition.

I cannot access the first partition (here F:) after I formatted that system partition with MyDefrag. In the beginning I could still access it as a non-booting partition but after Windows 7 during start up automatically recognised and addressed some problems with that partition I cannot access it all except when using a LINUX-based live rescue CD-ROM.

Any ideas how I can fix this?

ps: What do you mean by "privileges"?

I have now checked the HDD in an external USB drive and both CrystalDiskInfo and HD Tune report no errors.

See below:
http://imageshack.us/photo/my-images/193/crystaldiskinfohitachi1.jpg/

http://imageshack.us/photo/my-images/835/hdtunehitachi100gb.jpg/

Hello,

I have used MyDefrag following recommendations at http://www.techsupportalert.com/best-free-disk-de-fragmenter.htm.

I did run it on Win 7 64-bit in my main HDD and used the monthly system disk defrag option on the system disk with a Win XP 32-bit system on it that I had mounted in an ultrabay slot. Afterwards, I tried that disk in my main HDD slot and it did not boot. However, it worked still fine as an external/ultrabay HDD until this morning. When I booted my Win 7 system, it detected data corruption on the Win XP 32-bit partition and ran a fix. After this fix, I cannot access that anymore.

Please help me troubleshooting this.

Many thanks!