You would need to boot from your installation disk. How to tell you what to do next will depend on the actual version of Windows you are running. Can you provide more information on what you mean by explorer crashes and what version of windows is it?
I got my pc started with cmd in safemode, and i copied my files to my extern..
So my files are secure, but the main problem now is that I cannot copy my files to my other pc now, it says they are secured and cannot be copied..
windows xp sp 3
lenovo thinkpad r500
To copy your files to a flash file and reinstall windows you should really boot through a ubuntu live cd and copy the files while in ubuntu then reinstall windows. You can download the ubuntu live cd at http://www.ubuntu.com/download/ubuntu/download and to use it simply insert it into the computer then reboot or crash windows. After the computer reboots boot from the live cd (don't install it) and in the side panel there will be a picture of a folder. Click it. Then insert the flash drive. Copy all of the files from the other drives the the new drive that just appeared. Then reboot and take out the cd and put in the windows cd. Then reboot again and reinstall windows. Then after windows is installed your files *might* already be their but if their not then copy them back from the flash drive. That simple.