Laptop won't go past logo, what's wrong?

Lenovo Z710 laptop won't boot past the Lenovo logo. Can anyone tell me where the problem is and how can I fix it?

What did it do before this? What changed? Did you just buy it? We need more info and history on it.

If it just sits at a black screen, perhaps with a cursor you can't type in, then it hasn't found an operating system. Check the hard drive connections.

Most probable cause is the HDD is offline. This is usually because the hard drive has failed. If you wait 3-5 minutes, it may pop up a message asking to insert a boot media.
Other possibility is the HDD is still good, but the boot sectors are corrupted. You would need to run the Windows install disk to repair the boot sectors.