My computer is beeping two short beeps and will not boot. I have taken the back off the cpu. What do i need to do?

Suggest you remove the Ram Memory module/s, and clean the contact pins on the bottom, then reinstall.

What you hear are BIOS Beep Codes. The computers way of telling you something is wrong, and the area to look into for it.

This is Dell Support > Inspiron 531s desktop computer > Owners Manual > Troubleshooting > Beep Codes,

http://support.dell.com/support/edocs/systems/insp531s/en/OM/html/trouble.htm#wp1085300

After time, the contact pins on the bottom of the Ram Memory module/s ('Sticks') can develop corrosion.
The corrosion prevents a good contact.

According to the specifications, the Inspiron 531s uses DDR2 Sdram ram memory modules.

(DDR2 Sdram at a frequency rate of 533MegaHertz.
{533MHz)

DDR2 Sdram has 240 contact pins. 120 on each side.

The example below is DDR Sdram, which has 184 contact pins. 92 on each side.
The example is given to show you a close-up, of the gold plated contact pins I am referencing to,

http://en.wikipedia.org/wiki/File:Generic_DDR_Memory_%28Xytram%29.jpg

(You can left-click on the photo to enlarge)

Suggestion is to take a pencil eraser, and stroke in a downward fashion on each contact pin, towards the bottom of the ram memory module.
('Stick' is slang for Module)

(The top of the ram memory module, is above the black rectangular DRAM chips, on the side of the ram memory module.
The contact pins are on the bottom side)

If you use an eraser on the end of a pencil, refrain from letting the metal 'cap' touch the contact pins.

Refrain from touching the contact pins. (Static)
The body of the module, is coated with a see-through protective plastic.

After you have cleaned each contact pin, use air to remove the eraser dust.
You can use a can of compressed air for computers, or air pressure from your mouth may be sufficient.

NOTE*
BEFORE you begin to remove the ram memory modules, or reach inside your computer; and computer unplugged from power, observe Anti-Static precautions!

Anti-Static Precautions:

Your body carries Static electricity.

Static WILL fry out (Short Circuit), the delicate hardware components inside a computer.

(Hardware components examples, such as the Processor, Ram Memory, Harddrive, Motherboard, and graphics card/s if used)

To relieve your body of Static, TOUCH the metal frame of the open computer case.
(Computer unplugged from power)

Should you leave in the middle of working on your computer, upon your return be Sure to TOUCH the metal frame again.

An alternative method, (Best method actually), is to use an ESD wrist strap, and connect the alligator clip to the metal frame of the open computer case.
(Computer unplugged from power)

Electro Static Discharge.
One example of an ESD wrist strap,

http://www.radioshack.com/product/index.jsp?productId=2103245

Computer unplugged from power, all cables removed, I would lay the computer on a towel, on a table, and the case side that is open, facing up.

Easier to access those ram memory modules.

[ If you are not perfectly sure, where each cable plugs into on the back of your computer, now would be the time to make a drawing, and notes, before you unplug them.
Especially any audio cables that plug in ]

Removing and Installing Components: (Parts)

http://support.dell.com/support/edocs/systems/insp531s/en/OM/html/parts.htm#wp1603876

If you left-click on - System Board Components, you will get a basic idea of where the ram memory slots are located.
(4, 5, 6, and 7)

If you go back to the main menu, and left-click on
Memory, you will be guided in removing, and reinstalling the ram memory modules.

If you have any questions concerning this, or need more of a simplified explanation concerning anything I have stated, simply reply by posting in a Comment.
(Believe upper right of your page)

If cleaning the ram memory modules does not cure your problem, then I suggest you remove all ram memory modules, and reinsert one at a time

Test each ram memory module to see if there is a bad one. (Or if they all are bad)

Remove all ram memory modules, insert just one module in Slot 1.

(Place the unused ram memory modules, on a non-Static surface. Wood is one example of a non-Static surface)

On the System Board Components illustration, Slot 1 is referred to as DIMM 1.
(The number 5 points to DIMM 1)

The Processor reads Slot 1 first.

Procedure is, computer unplugged from power, install the ram memory module.
Plug the computer back into power.

Remember what I stated about Anti-Static Precautions.
To plug the computer into power, you may have to leave the seat you're sitting in.
TOUCH the metal frame upon your return.

Turn the computer on. See if the ram memory module is good. (No 2 Beeps)

Ram module checks out, shut the computer down normally. (Start> Turn Off Computer > Turn Off)
Unplug the computer from power.

Observe Anti-Static Precautions.
Remove the ram memory module. Place it on a non-Static surface. (Wood)

Insert the next ram memory module. Plug the computer back into power.
And so on.

I think this is the cause of RAM . Check your ram or try replacing another ram in your pc and check it.