How do I place the paper in the bottom tray?

Check the feed rollers located on the top bottom side where the tray is to slotted in. See if it's out of place. Have to secure it back in position.

1. Slide the paper-width guide to its widest position, and then pull out the paper tray extender. Figure 2: Move the paper guides
2. Insert plain white paper into the input tray with the short edge forward and the print side down. Slide the paper forward until it stops. Figure 3: Insert paper into the product
   CAUTION: Make sure the product is idle and silent when you load paper into the input tray. If the product is servicing the print cartridges or otherwise engaged in a task, the paper stop inside the device might not be in place. You could push the paper too far forward, causing the product to eject blank pages.
3. Slide the paper-width guide inward until it stops at the edge of the paper. Figure 4: Adjust the paper guides
   NOTE: Do not overload the input tray; make sure the stack of paper fits within the input tray and is no higher than the top of the paper-width guide.

Try these 2 links:
Both procedures need to be done for the printer to go back to normal operation state.
#1-
http://wss.support.xerox.com/GTConnect/UnifiedAcceptor/AddWebFramework.Main/site/XeroxProductSupport/product/product_4510/lang/en-US/region/region_US/source/DND/Xlang/en_US/Xcntry/USA/prodID/4510/KBlang/en/#!view-content/ViewContent/View/contentId/x_P4510_en-O1644
#2-
http://wss.support.xerox.com/GTConnect/UnifiedAcceptor/AddWebFramework.Main/site/XeroxProductSupport/product/product_4510/lang/en-US/region/region_US/source/DND/Xlang/en_US/Xcntry/USA/prodID/4510/KBlang/en/#!view-content/ViewContent/View/contentId/x_P4510_en-O4160

The 2840 can have an optional paper tray at the bottom of the printer.. perhaps that one is empty?
Otherwise, you place the paper on the open tray that drops down in front when you open it, and extend and adjust the guides.

You can use the paper cassette located at the bottom of the printer, on the front when the output paper tray is closed concealing the paper feed switch, the usb port and the cassette lamp.
1 Gently pull out the cassette from the printer.
2. Remove the cover from the cassette.
3. Place your paper in the cassette tray.
a. when using A5 or larger sized paper (non standard sized paper, pinch the tab and extend the cassette if needed.
b. legal sized paper is not loadable in the cassette
4. Do not load paper above the load limit mar4k.
5. Make sure the print side of the paper is facing down.
6. Align the paper stack against the right side of the cassette
7. Slide the paper guides so they fit the loaded paper stack.
8. The paper cassette will hold up to 150 sheets of plain paper, however you do not eant to stack any more than 50 sheets in the Paper Output Tray.
9. Reinsert the cassette into the printer. Then set the cover on the cassette. Now make sure the cassette is pushed al the way into the printer. (If long paper was used and the cassette was extended iy will now extend beyond the front of the printer
10. Prepare the paper output tray by opening the front cover and pulling out the tray extension until extended completely.
11. Press the paper feed switch so the cassette lamp lights.

You can slo select the paper source with the printer driver if you prefer .

Your model has two trays on the front. The bottom one of these two is where you load the blank paper.
1. Raise the output tray to load paper into the main input tray.
2. Slide the paper-width guide to its outermost position.
3. Tap a stack of paper on a flat surface to align the edges, and then check the paper for the following:
• Make sure it is free of rips, dust, wrinkles, and curled or bent edges.
• Make sure all the paper in the stack is the same size and type.
4. Insert the stack of paper into the main input tray with the short edge forward and the side to be printed down. Slide the stack of paper forward until it stops.
5. Slide the paper-width guide inward until it stops at the edge of the paper.
Do not overload the main input tray; make sure the stack of paper fits within the main input tray and is no higher than the top of the paper-width guide.
6. Lower the output tray.
7. Pull the output tray extender towards you, as far as it will go.

I hope this helps!

No, it sounds like you are doing fine. The machines are shipped with the paper tray in a "closed" position and they have to be expanded slightly (using the buttons on the bottom of the tray) to fit A4 size paper. The tray will then poke out about about 3 inches from the front off the machine as you described...this is quite correct and normal.

Hello sir; I guess you missing one place that's paper tray, try pull out may be paper hanging there, otherwise check the paper senser is in position.

Embarrisingly simple fix. The printer was pushed up close to our wall thus not allowing to the paper feeder sit back normally. Therefore the photo tray was not sitting correcly. Once placed in the proper position, it all worked fine.
Thanks for the response though.
Kind Regards.

Issue: "The selected paper size is not supported by your printer..." appears after selecting the Paper Size in the printer driver.
Solution: Use Fit-to-Page Printing (Windows)

Use Fit-to-Page Printing (Windows) The Fit-to-Page function automatically resizes the image to fit the size of the page being used. Letter size image data, for example, will automatically be printed on 4" x 6" size paper. Paper sizes larger than the printer can handle will be available on the Page Setup of the printer driver but will not print unless the Fit-to-Page function is enabled. Note: The Fit-to-Page Printing function is not available when Borderless Printing is selected.

1. Access the printing preferences by opening the printer Properties / Preferences:
   
   For Windows Vista
   • Click / Select 'Start' from the bottom left of the Windows screen, 'Control Panel', 'Hardware and Sound', and then click on 'Printers'. Note: If you are in 'Classic' view, Click 'Printers' directly from the 'Control Panel'.
   • Click your right mouse button on the listing for your printer, and then select 'Preferences' from the menu that appears.
     
   For Windows XP Home Edition
   
   • Click / Select 'Start' from the bottom left of the Windows screen, 'Control Panel,' 'Printers and Other Hardware,' and 'Printers and Faxes.'
   • Click your right mouse button on the listing for your printer, and then select 'Preferences' from the menu that appears.
   
   For Windows XP Professional Edition
   
   • Click 'Start' from the bottom left of the Windows screen, and 'Printers and Faxes.'
   • Click your right mouse button on the listing for your printer, and then select 'Preferences' from the menu that appears.
   
   For Windows 2000/Me/98
   
   • Click / Select 'Start' from the bottom left of the Windows screen, and 'Settings,' then 'Printers.'
   • Click your right mouse button on the listing for your printer, and then select 'Properties' from the menu that appears.
     
     
2. Click the Page Setup tab.
   
   
3. Specify the 'Fit-to-Page Printing' settings.
   
   
   
   
   (1) Select Fit-to-Page Printing.
   
   (2) Select the size of original document created in application program. Paper sizes larger than the printer can handle will be available.
   
   (3) Select the actual size of print media.
   
   
4. Click 'OK'.