If this is the virus infection then you can try Rescue Disk, you can download from Avira or Kaspersky
http://www.avira.com/en/support-download-avira-antivir-rescue-system
http://support.kaspersky.com/viruses/rescuedisk?level=2
After download burn it to CD/DVD or usb drive, boot it and scan..
Kaspersky Rescue Disk User Guide..
http://support.kaspersky.com/downloads/guides/kasp10.0_rescuedisk_en.pdf
Can you update what is your laptop brands and model, because your laptop may be have recovery partition and you can reinstall windows from there.....
If you are sure your laptop do not have recovery partition, then follow the link to reinstall your windows...
http://www.sevenforums.com/tutorials/1649-clean-install-windows-7-a.html
To reinstall you need the Windows Installation Disc and a genuine product key.....If you do not have the disc, you can download the windows iso file and burn to CD or usb drive....make sure you have the product key.....
http://www.askvg.com/direct-download-links-download-official-original-and-untouched-windows-7-iso-32-bit-and-64-bit/
*UPDATE*
Do you mean you can boot into windows and you see blank screen and blinking cursor after login....or you cannot boot into windows at all....
*UPDATE*
I think your Asus netbook have recovery partition, you can restore/reset you windows....but all of you data (program, document...) will be delete.
Maybe this can help you.
http://en.kioskea.net/faq/4162-restore-an-asus-netbook-to-factory-settings