Plese help my ibm think pad r51 turns on and goes though the start up and at the end this came up:

A problem has been detected and windows has been shut down to prevent damage to your computer

UNMOUNTABLE_BOOT_VOLUME

If this si the first time you've seen this stop error screen restart your computer. If this screen appears again, follow thes steps:
Check to make sure any new hardware of software is properly installed. If this is a new installation ask you hardware or software nanufacturer for any windows updates you might need.
If problems continue, disable or remove any newly installed hardware or software. Disable BIOS menory options such as caching or shadowing. If you need to use safe mode to renowe or disable components, restart you computer press F8 to select Advanced startup opions, and then select safe mode.
Technical niformation:
*** STOP: 0x0000000ED (0x812DAA68,0xc0000006,0x00000000,0x00000000)


Then it just rebots and starts all over again and comes back to that scren and I can't even start it in safe mode.
PLEASE HELP ME!

This error indicates an issue with the hard drive, normally a hardware failure.
Time for a replacement.

But why would it do this all of a suden? I just turned it off and a day later I tried to turn it on so why?

Dvtix

Who's to say.
Electronics fail all the time for a variety of reasons, most unexplained.

Can a hard drive make a computer faster too?and how much do they cost?

A hard drive stores your programs and data. a faster hard drive can speed up program load times and data reads. They aren't too expensive. A 320G drive for a laptop is probably less than $100.

However, if you replace the drive you will need to have a copy of the Windows install CD as well as all your program installation files. And any data will be lost.

Ok that's to bad