are you able to boot in safe mode?
if so, download nirsoft produkey to an USB flash drive
http://www.nirsoft.net/utils/product_cd_key_viewer.html
then press F8 at your laptop boot and choose safe mode from list
once at desktop, plug your USB flash drive, run produkey
if you are not able to boot, you can take off the HDD from your laptop, connect it to another PC using an USB HDD bay and find the product key using produkey (just be sure to select the correct HDD)