If you can't switch it on, there seems to be some hardware problem. If it turns on but don't properly boot, you may have some corrupted system files. This is a software, OS, problem.
Next, to recover your data, it should be as simple as removing the drive from your computer and connecting it to another computer as an additional drive.
The other computer can be another Windows based PC, a PC running Linux or even a Mac (yes, a currect Mac CAN access an NTFS formated drive).
I hope that you did NOT use bitlocker, as it's hardware locked to specificaly make it impossible to access the crypted data by transfering the drive in another computer.
BitLocker is available in Windows 7 Pro and Ultimate.
In this case, your only hope it to attempt to repair your Windows installation.
Get an installation DVD and use it to boot. It CAN be a version downloaded from a Peer 2 Peer network. Using such a version to repair a legitimate install is legitimate.
Once you have booted from the DVD, start the install process and chose the "Update" option when asked.
This will restore/replace any damaged or missing system file while preserving yopur data.
Electro, June 2012