Yellow stripes on imac (early 2009) display - Apple 20" iMac Desktop

On your Mac click on the top left Apple icon and click about this Mac. Then click on software updates.

Go to Crucial.com and enter your MAC details

Early 2009. You can check your mac's full info at
http://www.appleserialnumberinfo.com/

• iMac (Mid-2007 or later)
• MacBook (13-inch Aluminum, Late 2008), (13-inch, Early 2009 or later). What model of the computer are you using? To down load go to Software update under the Apple ( black colored icon ) pull down menu

Hard to say without knowing exactly what Mac you have and what specs, but most likely reason would be your system doesn't meet the requirements (From Apple support site) - To install Mavericks, you need one of these Macs:

• iMac (Mid-2007 or later)
• MacBook (13-inch Aluminum, Late 2008), (13-inch, Early 2009 or later)
• MacBook Pro (13-inch, Mid-2009 or later),
• MacBook Pro (15-inch or 17-inch, Mid/Late 2007 or later)
• MacBook Air (Late 2008 or later)
• Mac mini (Early 2009 or later)
• Mac Pro (Early 2008 or later)
• Xserve (Early 2009)

Your Mac also needs:

• OS X Mountain Lion, Lion, or Snow Leopard v10.6.8 already installed
• 2 GB or more of memory
• 8 GB or more of available space

Please provide more information.
To what would you like to upgrade it?

Since OSX Mavericks was just announced, I'm going to assume that's what you're wanting to upgrade to.

Not all Macs can run Mavericks.

Mavericks Capable Macs

Mavericks, like its predecessor Mountain Lion, requires one of the following Macs with at least 2 GB of RAM and 8 GB of available hard drive space:

• iMac (Mid 2007 or newer)
• MacBook (Late 2008 Aluminum, or Early 2009 or newer)
• MacBook Air (Late 2008 or newer)
• MacBook Pro (Mid/Late 2007 or newer)
• Mac mini (Early 2009 or newer)
• Mac Pro (Early 2008 or newer)
• Xserve (Early 2009)

If your Mac isn't one of the ones listed above, you won't be able to upgrade.

If you have an iMac, MacBook, MacBook Pro, or Mac mini model that was originally released in Early/Mid 2006, the latest version of Mac OS X your system supports is Snow Leopard.

http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard

You must have the following computer to download Mountain Lion:

iMac (Mid 2007 or newer)
MacBook (Late 2008 Aluminum, or Early 2009 or newer)
MacBook Pro (Mid/Late 2007 or newer)
MacBook Air (Late 2008 or newer)
Mac mini (Early 2009 or newer)
Mac Pro (Early 2008 or newer)
Xserve (Early 2009)

Once that is done, you must be updated to the most recent version of either Snow Leopard or Lion. If you don't have either of these operating systems (which is highly unlikely considering the other computers should have them, but I digress) then you will need to get them before Mountain Lion.

After that, go to the Apple Store and download Mountain Lion!

It is best to check with an Apple store, assuming there is one within 100 miles or so, especially if you are under AppleCare, yet--unlikely. My 20" iMac G5 gave up the ghost a year ago. Their cost to repair/replace the logic board was >$800. I've heard 3rd party as low as ~$500. I decide to change to an MacBook 13" (Early 2009 white, then current) and love its convenience.
Try the Macintosh boards where I have posted http://discussions.apple.com/category.jspa?categoryID=134 "Apple - Support - Discussions - iMac G5". No luck for me though. If you have the early G5 that I have, pull power plug and any cables, place face on non-scratching surface, rotate 1/2(?) turn the 3 screws on the bottom, lift off the back and stand, use the power cord to try to start it. There is a button for this but varies with models. If only one LED lights or 2 for a short time you may have my problem. First, after the back is off check if the capacitor tops are bulging. If so that is a known repair, but its coverage expired.
-Ken

Go to www.hmaservice.com and register( Vehicle by VIN). Afterward, you have access to shop manuals, service bulletins, wiring diagrams, etc. about your vehicle.

first try your monitpor to other computer to see from where the problem come and then you will find who quilty