can you boot this machine from a DVD,
If you can then use a stand alone Backup - you can download a trial of acronis or other software - to backup to external drive and then WIPE the laptops HDD. You can use GPARTED or similar to force a wipe of the HDD.
Now you can restore the "initial configuration" if the laptop came with pre-installed stuff - if not just send the laptop for repair with an empty disc.
Technicians will have bootable OS'es etc for repairing the computer -- when you get it back make sure they haven't charged you for "re-installing an OS".
If the system isn't bootable then remove the HDD and insert another one if you can --laptop HDD's are generally easy to remove and swap.
Enc pic of typical SATA laptop HDD.