As stated the Acer Veriton 6800 desktop computer, uses the standard ATX form factor power supply, found in over 85 percent of personal computers out there.
For a PSU (Power Supply Unit), the form factor refers to the size, and shape of the PSU's case.
The ATX form factor is approximately 6 inches Wide, 6 inches Long, and 3-1/2 inches Tall.
(15.24cm Wide, 15.24cm Long, and 8.89cm Tall ]
Working on a table, computer unplugged from power, and all cables removed from the computer tower.
Observe Anti-Static Precautions BEFORE you reach inside your computer.
Your body carries Static electricity.
Static WILL fry out (Short Circuit), the delicate hardware components inside a computer.
Work on a table. It is more convenient for some to work on a carpet floor. This equals NO. A carpet floor is a Static nightmare.
Same with working on a bed.
Computer unplugged from power, computer case open.
TOUCH the metal frame of the open computer case, to relieve your body of Static.
Should you get up, and walk away in the middle of working on your computer, upon your return be SURE to touch the metal frame again.
A better method is to buy, and use an ESD wrist strap.
(Electro Static Discharge)
The ESD wrist strap has a plate of metal that contacts the skin of your wrist.
In turn, the metal plate is connected to a cable, with an alligator clip on the end.
The alligator clip is attached to the metal frame, of the open computer case.
This is an example of an ESD wrist strap,http://www.radioshack.com/product/index.jsp?productId=2103245
How to open the computer case:http://www.acersupport.com/acerpanam/desktop/0000/Acer/Veriton6800/Veriton6800ul.shtml
Left-click on - Veriton 5800/6800/7800 User's Guide (EN)
This is a PDF file. (The computer you are using now has Adobe Reader on it, which uses PDF files)
Give the file time to download. Takes a few seconds to see the first page, and additional time for the file to fully download.
Page 60 deals with removing the computer cover.
Facing the front of your computer, the left Side Panel removes.
Looking at the back of the computer, and towards that Side Panel, there are two Thumbscrews to loosen.
One towards the top, and one towards the bottom, on the edge of the Side Panel.
Turn the Thumbscrews to the Left to loosen.
Towards the bottom Thumbscrew, there is also a T-shaped slide release lever.
Use the formed 'Bump' at the end of the Side Panel for your fingers, and press the slide release lever down, while pulling back on the Side Panel.
The Side Panel will only slide back approximately 1 inch, (2.54cm), then the Side Cover's top is tilted to the outside, and the Side Cover is lifted up, and out.
Generally there are 4 screws to remove from the Power Supply, on the back side of the computer. There are 3 located in the corners of the Power Supply's case, and another one slightly offset.
I don't see that with this model, judging by the rear photo presented in the PDF file.
Probably has a plastic bracket on the inside of the computer, that holds the Power Supply in place.
Located at the top of the Power Supply's case, and towards the front of the computer.
Usually there is a plastic locking tab that is moved slightly, and allows part of the bracket to slide to the side, releasing the Power Supply case from the computer case.
Some just have a small metal bracket, that has a single screw holding the bracket in place.
All of the power cables generally are gently wiggled side to side, as they are pulled out, except for two power cables.
(ONLY wiggle, and pull on the connectors, and Not on the cables)
There are two power cables that have a locking tab on the side, that must be released first, before the power cable can be removed.
A) The 24-pin ATX main power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain24
(To the right side of the ram memory slots)
B) The 4-pin ATX +12 Volt power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#atx12v4
(To the top right of the Processor socket.
Page 62 shows the layout of the motherboard)
The plastic locking tab is hinged in the middle, and operates just like a seesaw on a playground.
The top of the lock is squeezed in to release the lock.
(Squeezing the top of the lock in towards the connector, pulls the bottom hooked end of the lock, out of a tab on the motherboard connector)
Example of a decent, reliable ATX PSU,http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3276574&CatId=1079
You don't have to spend too much to get an affordable, reliable PSU, but if you spend too little, you may wind up with the same problem in the near future.
If you have any further questions regarding this, or anything I have stated, please post in a Comment.