It sounds like your optical drive has failed. You may still be covered under the first year of apples limited warranty, if you are, just take it in to the apple store or any apple authorized service department and they will be able to diagnose and replace it for you. Hope this helps!
It does sound like your video card is failing. The good news is that the video card is separate from the logic board, therefore you can just replace the video card. Make sure that you find out exactly which video card is in your iMac, ideally getting the apple part number, since there are several different models of this iMac as well as several different model video cards within each of the models. If you provide your serial number I can get you the correct part number for it. Another thing to consider is that replacing the video card in these iMacs is not a simple repair at all and if you are not careful you can mess something else up in the process. Doing this repair at a shop should cost you around $150 in labor and ball park around $200-$300 for the video card. Hope this helps!
Make sure that you are using the correct tool, it should be a "000" precision tool, you might be able to get away with a "00". Its important that you use the right tool so that you can apply a good amount of pressure and try to turn it without the screw driver slipping out of the head of the screw. Hope this helps!
Replacing the hard drive in the eMac is not easy at all and is not considered a CIP - "customer installable part". It has been years since Ive had to work on one of these but from what I remember you have to take the entire eMac apart. I do not recommend that you do this unless you have some experience working on them. Apple recommends discharging the CRT as it can shock you and/or implode and is dangerous to deal with. Here is some info that I found: http://www.everymac.com/systems/apple/em...-replace-or-upgrade-hard-drive-expansion.html Hope this helps!
I dont think that there is a way to remove that fan without taking apart the enclosure and taking apart the enclosure is not possible, without damaging it, as it is put together with rivets. There are some parts that when they go bad just require an enclosure replacement, this is one of those parts. Hope this helps!
This issue can be caused by a couple of different parts. It can be caused by a bad LVDS cable (video cable), a bad LCD, or a bad logic board. The time and money that you will spend, unless you have another same macbook pro, is not worth it. You may just considering using it as a desktop with an external display, keyboard, and mouse. Apple offers a flat-rate option that would repair this problem for around $300-$400 but this model is too old for that option. Another option is to go online and buy a used macbook pro, you can find a comparable one for around $300-$400. Apples refurbished computers are also a good deal. Hope this helps!
Upgrading the processor and graphics card in any iMac is not something that is typically done or possible, in most cases. In order to upgrade your processor you would need to replace the entire logic board, which cost a lot of money and not worth doing. You may be able to upgrade the video card but you would have to buy a video card from apple that would be compatible with your iMac and again it would be very expensive. If you provide your serial number I can give you a better idea what options there are and pricing. Hope this helps!
If there are some keys that are not working then the solution is to replace the keyboard. Replacing the keyboard on that model iBook is fairly simple. Here is a link that I found from ifix: iBook G4 12" Keyboard Hope this helps!