Hi,
Don't you just hate it when something like this happens?
The simplest thing to try is a fresh install of windows without getting to bogged down.
BOOT up and go through the initial stages of Installing Windows 7 from the DVD
It should load files and when it asks you what you want to do you need to do a Custom Install
A screen will come up showing you your hard drive, Highlight the Drive then delete the partition. Do the same for the smaller partition (about 100 mb) which is System Reserved. Ignore all warnings. You will then have just one option available which is to create a new partition, don't change any of the figures just click yes. Once you have done this your Hard Drive will be clean and you should be able to install Windows without a problem.
Unless you want to use a specific language for your on screen Windows menus and interfaces, you don't need to download or install any language packs. If however, you want to run your PC and have the Windows menus etc., in Dutch, German, Japanese then you should only download the language pack that you need. When it has downloaded and installed, you will need to reboot the PC.
When the PC reboots you will get a message about reconfiguring windows or configuring windows updates, this is normal as it is integrating the Language Pack into the system so don't worry.
Some things to consider regarding Anti Virus and other spyware programmes. It is not a good idea to have these running when you are installing programmes as they can throw up false positives and corrupt the install. I have built a lot of PC's and, I don't install these programmes until after I have installed the OS, installed the drivers that are needed, downloaded all the updates and am happy that the system is running fine. Whenever I install a new programme that I know is OK because I brought it or have used it before, I make sure that I disable the Antivirus before I begin the install.
Hope this helps