Not able to install software or updates

I have a Dell Studio 1737 running Vista 64 Bit that I purchased used I erased some files that belonged to the former owner trying to change the Computer to my name. And ever since I’m not able to install any programs Software or any updates. It starts installing Software and finishes but it does not finished loading, because when you try to run the program it start and stops in the middle. It only loaded part of the program where it starts but will not run. Tried installing sp2 and it failed, not installed. So how do I get it install the software. It also will not let me do a Factory reinstall. Also let me say that I know about just enough to get me into trouble as you can see. I would appreciate if some one could Help me Please. Thank you Walt

I would log in as Administrator and create a new user account or do a reinstall of Windows, to start from scratch. See Tutorials Forum User Accounts to create the hidden Administrator account,