It is looking to load the OS from a removable source or the hard drive. I don't know what the HD geometry would be on that right now.
I would need more information. If you have an OS loaded and you get a boot sector error message, then the boot sector is either corrupt, missing, or has the wrong address.
If I am understanding you correctly, you do not have an OS, therefore, you cannot boot your system. If you want, you can get a free linux OS (which I would not recommend this since you claim that "Im not very good with computers."
So go look for a cheap copy of Windows XP Home or Pro, maybe even the OEM version (whici I believe is bereft of a few files). You can get an OEM version for around $140.
You will then have to install Windows and configure the system, which encompasses a lot of little steps like updates, drivers, etc.
Hope this helps. Let me know.