Can you use iMac in target display mode with a Hp laptop

1) Users, not Apple, accidentally discovered that a limited number of 2009 and 2010 27-inch iMacs would work with some non-Apple products. 

2) Apple never intended, documented, nor supported this "happenstance."

3) That quirk of video hardware stopped when the 2011 models appeared. NOTHING newer even accidentally supported non-Apple devices through Target Display Mode. 

What you are trying to do, only worked with the Late 2009 and Mid 2010 27" iMac's using a Mini DisplayPort cable. Even then, it was hit and miss with a PC's that supported Mini DisplayPort for display output.

Allan Jones wrote:

1) Users, not Apple, accidentally discovered that a limited number of 2009 and 2010 27-inch iMacs would work with some non-Apple products. 

Apple's Technical Specifications for the Late 2009 iMacs say "27-inch models also support input from external DisplayPort sources (adapters sold separately). There are no fine-print footnotes saying the machines "sort-of take DisplayPort input" or take it from other Macs only. Apple's specifications for their 27-inch Mid 2010 iMacs say the same thing.

That feature was a selling point for Late 2009 iMacs. At the time they came out, a 27" 2560x1440 monitor from Dell cost $1,000 – $1,200 (depending on whether it was on sale). Not the $350 or less one might cost today.

The Technical Specifications for the 2011 iMacs don't mention the video input feature, perhaps because the need for Thunderbolt input made the feature much useful as a selling point. In the early days, very few Macs, and just about no PCs, would have had the Thunderbolt output needed to use the display of an iMac operating in Thunderbolt Target Display Mode.

This article only mentions Mac to Mac. Use your iMac as a display with target display mode - Apple Support