From what I've read in this forum, it is most likely a hardware issue, in your case a bad LVDS cable connection, bad LVDS cable, or less likely, a bad display. Video displayed on your external monitor indicates the Video Graphics Adapter is functioning properly.
Some have
temporarily resolved this issue by unplugging, removing the battery and all peripheral devices, holding the Power-On button down for 30 seconds, then plugging in and booting the laptop. Others have wiggled the top of the laptop or pressed on different areas to get video to appear on the laptop display. However, the issue usually returns...
Some have reported they resolved the issue by completely disassembling and reassembling the laptop. This action will void the warranty, so it is not recommended for new laptops.
My recommendation would be to exchange your defective laptop for a new one or accept a complete refund if an exchange was not possible due to lack of a replacement.
G74SX-A1 - stock hardware - BIOS 202 - 2nd Monitor VISIO VF551XVT