how do i reinstall windows 7?

[capexpenses]

my computer did not come with installation disk.  I purchased it from BJS.  How do I reinstall the original version of Windows 7.  I am trying to run service pack 1 and am unable to.  Also, windows installer is not working after a recent update.

[HaggisCat]

Before going to the drastic procedure of reinstalling the OS, have you tried doing a Windows restore point to fix the problems.

 Go back as far as you can and try to run Windows update again.

 Also, what's the model number of the computer ?

[capexpenses]

Already tried that and now more items do not work.

[HaggisCat]

There should be a recovery partiton on the hard drive. The easiat way to run it is to shut and on boot up start tapping the f11 key.

 Be sure and back up all you personal stuff first as this will wipe all that out.