Short version: w7 setup wouldn't load, Linux systems would. This is what I did to my system, in steps:

1) I had W7 installed but after meddling with the system, I could not reopen W7 - blue screen.
2) So I tried to reinstall from the cd, and exactly after the first windows setup bar finishes and those 4 colours reunite to open the rest of the setup - I receive a blue screen saying Unknown hard error ntdll.dll missing. I tried installing XP, and received a black screen saying the setup closed because a problem with my hd was found - something about hd not properly finished.
3) So I used Darik's Boot And Nuke and ERASED everything on it. After this the same problems with the 2 cd's. I tried all kind of tools, test from Partition Magic cd and tried to re-partition my hd propper. Nothing worked.
4) So I installed Linux Mint 15 - and worked.
5) But W7 is what I'd preffer - and still setup wouldn't load. Not even in Oracle VIRTUALBOX run through Linux.

Question:

What is wrong with my hard DRIVE that Linux can install, I have full acces to my hd from Linux or LiveCd's but Windows 7 would not install on it ?Let me try to recap this.
You had a working dual boot Windows 7 and Linux system.
You meddled and something happened to Windows 7.
You even tried to install XP.
You erased everything with some utility.
Now only Linux with work.
Are the above statements represent what happened?

You may have a rare problem with that had drive. Now is then time to try to install windows 7 on a clean hard drive that has been prepped for a PC. Rather then try using the save drive over again, try another drive. This will eliminate the hard drive as being the issue.




Thank you for your reply. No, the initial situation was: I had only w7 installed. I meddled and now only Linux works. There wasn't a dual boot. Do you know of any hard drive requirement that W7 had and Linux did not ? I suspect it is something wrong with something some data on the drive that enables it to boot normally for windows. I don't know what is it, I already tried to heal MBR, though I don't exactly know what that is. A HDD set up in Linux is not compatible with Windows. Unless there was an compatibility option chosen in the Linux setup.
In Windows, a HDD must be initialized and then formatted in NTFS. You can not initialize the HDD unless all partitions have been destroyed.

The MBR for Windows 7 is newly defined by Microsoft and DIFFERS from fierier definitions. The disc has to be set the way Windows wants it.
The current boot manager for Linux is GRUB. It is rather complex and beyhound the scope of this post. (GRUB can not program your microwave oven, but otherwise it can do a lots of things.)
Here is a post about Linux / Windows boot conflicts.
Windows Overwrites Linux Boot Manager
I still recommend you use another HDD. There is a small chance something happened to the HDD. Use another PC to test a spare HDD.