Tabatot, please print out the instructions in thsi tutorial:-
Repair Install
Put a copy of Windows 7 Ultimate 32bit Installation DVD into your DVD/CD drive(Important:- This does NOT work with a Samsung recovery disk) If you do not have a copy of the installation disk you will need to either get on or borrow one.
Then switch on but as you do keep tapping "f2", this will allow you to access your BIOS settings. When the screen comes on select the tab that allows you to choose the boot order and set the first boot device to "DVD/CD" and then select "f10" to save your settings. Reboot and this should then boot your system from the installation dvd.
Once it has come to the selection screen, follow exactly the repair install instructions you printed earlier. Then please let us know how you got on with it.