Ompaq cq50 blank screen

See if removing the disk produces a response: "No disk or non-system disk, replace and press any key" or something of this sort. That will rule out the hdd failure, alternatively you can try the hdd in an external USB casing to see if it works. Computers with broken/malfunctioning hdds very often hang, bit will come back to life if hdd is disconnected. If the hdd is fine, you most likely will have a memory or a motherboard problem. Removing/replacing or changing position of the memory may help, sometimes they have loose connectors (mind static, earth yourself before touching any of the components of your laptop).