Q: When turning my MacBook Pro on I get the start up noise but nothing more

Have you seen this. About the screens you see when your Mac starts up - Apple Support

What model / year of MacBook Pro are you using?

Mac OS X- Gray screen appears during startup

Tackle your Mac booting to a gray screen | MacIssues

This usually indicates an internal hardware problem of malfunctioning screen. Do you experience the same result if you boot from the installer disc that came with the computer or with the retail Snow Leopard DVD if it can boot your model. It would help to provide the exact model you have: To find the model identifier open System Profiler in the Utilities folder. It's displayed in the panel on the right. Please provide the amount of RAM you have installed. Have you tried reinstalling OS X? See below:

Reinstall OS X Without Erasing the Drive

Repair the Hard Drive and Permissions

Boot from your Snow Leopard Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu. After Disk Utility loads select your hard drive's out-dented entry (mfgr.'s ID and drive size) from the the side list.  In the Disk Utility status area you will see an entry for the S.M.A.R.T. status of the hard drive.  If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (indented sub-entry, usually Macintosh HD,) click on the First Aid tab, then click on the Repair Disk button. If Disk Utility reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit Disk Utility.

If Disk Utility reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.

Reinstall Snow Leopard

If the drive is OK then quit Disk Utility; return to the installer.  Proceed with reinstalling OS X.  Note that the Snow Leopard installer will not erase your drive or disturb your files.  After installing a fresh copy of OS X the installer will move your Home folder, third-party applications, support items, and network preferences into the newly installed system.

Download and install Mac OS X 10.6.8 Update Combo v1.1.