The line is caused by the traces going bad in the video cable going from the LCD the the main board. They wear out over time from the cable having to flex from opening and closing the lid. It will only get worse over time. You can get a new cable off of ebay for arounf $25.00. Depending on the laptop, depends on how hard it is to replace.
Considering its an HP laptop I would just contact them for a repair, if you didn't damage it in any way they will repair it under warranty (if you're still in warranty)
The line is caused by the traces going bad in the video cable going from the LCD the the main board. They wear out over time from the cable having to flex from opening and closing the lid. It will only get worse over time. You can get a new cable off of ebay for arounf $25.00. Depending on the laptop, depends on how hard it is to replace.
Considering its an HP laptop I would just contact them for a repair, if you didn't damage it in any way they will repair it under warranty (if you're still in warranty)