Notebooks, netbooks or laptops as a general rule... don't have user replaceable video cards.

Key word "user"

Both the above answers are right.
If the computer is still under warranty return it to a HP service center through HP channels or call tech support. The video card in laptops is nearly always integrated into the main board. Replacing the main board is usually expensive and HP has some control on their service parts so a motherboard is only available from authorized service vendors or on the gray - black market. So you will buy the part and pay for installation. At this point it is advisable to compare the cost of repairs against the cost of replacing the laptop remember to consider the age of the computer and your plans for replacing the computer if it were not to have had this issue. If the laptop is more than two years old and out of warranty replacement appears to be the most cost effective approach, considering the cost of both a non warranty repair and replacement averaged over the lifetime of both the new andf repaired computer.