I have a computer with windows xp professional, I gave it to my sister in law and she deleted some system files and now it doesn't work. I don't have the windows cds anymore so i need to find a free operating system like linux but i really dont understand it. could someone please explain it and where to get it. Or maybe something else i could do would be helpful.
Alright, first of all you should be aware that Linux is not a free version of Windows. It is a completely different operating system, and Windows programs are not designed to work on it. Using an API like Wine it is possible to get a large proportion of Windows programs to work, but not all. Therefore, if you are after a gaming machine, Linux won't cut it. For anything else though, there are plenty of alternatives or Linux versions that equal or exceed their Windows alternatives.
Right, so where to get it? The question first, is what to get? From what you're saying, I'd advise against distributions like Slackware, Gentoo, Linux From Scratch and Damn Small Linux. My advice is to go for Fedora, OpenSuse, Ubuntu or Debian. I and many others would advise Ubuntu for a first dig into Linux, because it comes with a complete suite of applications, the installer fits onto one standard CD, and it's pretty user friendly.
What you should do is download the latest version of whatever distribution you choose. In the case of Ubuntu, you can get it by downloading it from their website, or requesting a free CD. If you download it (this is true for all distributions), you will get a .iso image which you then need to burn to a blank CD with some CD burning software. Note that you can't just copy the ISO file to the CD and click "burn", you actually have to burn the image itself. There's an important difference. A good CD burning utility for Windows is Active@ ISO Burner. I would advise against using Nero, because some versions try to be too clever and fail utterly at burning bootable CDs.
Okay, now for the moment of truth. Boot up the computer you want to install Linux on with the CD that you've just burned already inserted. If you don't see any difference, then one of two things has happened:
1) Your BIOS isn't configured properly. Normally when you boot up you see something like "Press F2 to enter Setup" on the very first screen, before the operating system loads. Press whatever key it says at that point, or if it doesn't say anything just try F2, F8, Del, then all the other F keys, in that order. Eventually you'll reach the BIOS configuration screen. Go to the "boot" section, and set your CD drive to have a higher boot priority than your hard disk.
2) You didn't burn the CD properly. Under Windows, insert the CD and check its contents. If you see just one file, you have done it wrong! A whole bunch of files and folders is what you're after.
From here on, it's very easy. It varies between distributions, so I'll describe the procedure with Ubuntu. You'll be asked to choose your locale and then what you want to do. Choose the default option, "Try ubuntu without any change to your computer" and after a few minutes you will be presented with a fully working (but very slow) operating system. This is the Live CD feature of Ubuntu that some distributions (but not all) have, and with it you can try it out before installing. If you look under "Places", you'll find your hard disk and you'll be able to look at the files on there. If you plug in a USB device you can then back up any files you want to keep but couldn't get at because Windows wouldn't boot!
Once you're done backing stuff up, you must safely remove both your USB device AND your hard drive! Yep, you can't continue with a hard disk partition mounted. Both should appear as an icon on your desktop, so right-click each and click "unmount". When you unmount the USB stick, that's like choosing "Safely remove" in Windows, and you can just pull it out. When you unmount the hard disk, you can then proceed with the installation. Go ahead and click "Install".
Follow the steps through. When you get to partitioning, you will probably want to choose Guided partitioning (use entire disk). I'd strongly recommend selecting the option to have a separate /home partition, that way all your data will be on its own partition and you don't need to go through a tedious backup process if you ever reinstall. If you want to have a really fast system, you could opt to make your main OS partition ext4 instead of the default ext3, but there may be a risk of data loss. If you do, look at the next paragraph, otherwise skip it.
If you feel like a super-snappy system, this is the thing to go for. By default, your filesystem is made using ext3, which is known to be very stable. But if you want to try out ext4, which is less stable but a lot faster, you can. Choose "Manual" partitioning and you are shown a screen. First thing to do is delete all existing partitions. Then "Add" a new one, choose "Primary partition" and make it ext4, mounted on /, and give it anything from 8 to 10 gigabytes in size. Then click "Add" again, create another primary partition, make it ext3 (NOT ext4 - the difference here is minimal and you want the reliability of ext3 for your data files, all of which go in here), mounted on /home, and make it take up the rest of your hard disk minus about 2 gigabytes. Finally, click "Add" for a third time and use the rest of your space to create a partition of the "swap" type. Then click Next.
Finally, you will be shown a summary of what's going to happen, and you can start the installation. Go for it, it will take anything from 10 to 30 minutes depending on the speed of your computer. When it's done, reboot and remove the disk, and you'll boot into your new Ubuntu/Linux desktop. Check to see that everything's working - it may recommend that you install a driver for your graphics card, just let it do its thing. Apart from that, you should find that everything works out of the box. The only other thing that might be a possible problem is wireless internet, so just check that out to see if you can connect or not if you use wireless. Wired internet always works (99.999% of the time).
Wow... An extensive explanation, and very useful. Now, I understood many things about GNU/Linux OS.