What kind of motherboard is in my acer aspire AST 180-UA381B- It has 4 RAM slots and when i tried to add the 3rd it whent nuts with beeps

The motherboard for the Acer Aspire t180-UA381B desktop computer, is supposed to be based on the Foxconn AM2 MCP61S series of motherboards.

Based on one of these two with some small modifications,

http://www.foxconnchannel.com/product/Motherboards/chipset.aspx?socket_id=en-us0000007&chipset_id=en-us0000090&Socket=Socket+AM2&Chipset=MCP61S

(You can click on Specifications for each motherboard, then click on the photo of the motherboard to enlarge.
After clicking it takes a second, then a small window comes up on the left. Click on the Maximize icon. { Icon to the left of the Red X)

There are Four ram memory slots.

2 of the ram memory slots make up one Channel.
The other 2 ram memory slots make up the other Channel.

When you use ram memory that has the SAME specifications, in the SAME channel, you are using the ram memory in Dual Channel.

[ And I mean the SAME.
Sometimes this means from the same manufacturer.

Same type, same frequency rate, {'Speed'}, same density, same chip configuration, same ram timings, same voltage, Unbuffered, and Non-ECC ]

When you install ram memory in a Dual Channel configuration, the two ram memory modules ('Sticks'), 'piggyback' off of each other.
They essentially team up on the task.

In the past this was thought to increase ram memory 'power' up to 30 percent.

Extensive testing has proven this to be a fallacy.
2 to 3 percent is more accurate.

NOW;
The Maximum Total Amount for the motherboard, (Relying, if it does indeed follow the specs of the Foxconn motherboards linked above), is 4GB.

[ According to Acer Support, the above criteria follows suit,

http://support.acer.com/acerpanam/desktop/0000/Acer/AspireT180/AspireT180sp2.shtml ]

EACH ram slot's Maximum Amount is 1GB.

If, perse, you have 1GB in each of the first 2 ram slots that are closest to the Processor, (Same channel. Same color), and are trying to install a ram memory module of 2 GB in the 3rd slot, this isn't going to work.

If you are trying to install a ram memory module that is of a different frequency rate ('Speed'), it may also not work.

Example: DDR2 Sdram at 667Mhz, (PC2-5300), and DDR2 Sdram at 1066MHz, (PC2-8500)

Further example:
You have 2 sticks of PC2-5300 at a 1GB amount in Slots 1 and 2.
You try to install a stick of PC2-6400, or PC2-8500 of 1GB in Slot 3.

Not happening.

BIOS will try to clock down the faster ram memory to the slower ram memory that is installed.
One step up, (PC2-5300 to PC2-6400 for example), may work.

Two steps up will not.
(Example PC2-5300 to PC2-8500)

It also depends on what Processor you have installed.
Ram memory typically operates at half of the FSB frequency rate, that the Processor's FSB does.

According to Acer Support, an AMD Athlon 64 X2 processor, or an AMD Athlon 64 processor, or an AMD Sempron processor can be installed.

I suggest using CPU-Z from CPUID.com, and find out the exact specs of the hardware inside your computer. (It's free, although they do accept donations}

As stated, Crucial has a good system scan analyzer, but has been found to be unreliable, or doesn't work in some circumstances.

You also need to know the specifications of the ram memory you are installing.

Comparing stock performance ram memory, to high performance ram memory.

Some of the high performance ram memory uses a higher voltage, for one.
For two the ram timings are different.
For three the density of the DRAM chips are different.
For four the Chip Configuration is different.

Just some of the parameters that can vary.

Stock voltage for DDR2 Sdram set by JEDEC at 1.8 Volts.
This is what is set as a default voltage in your computer, for your ram memory.
Use high performance ram memory that may use 2.1 volts, and there's going to be a problem.

Also if you purchased this ram memory from Ebay, good luck.

Need to know WHAT ram memory you have installed in Slot 1 and 2.
Give me any numbers off of the ram memory module that you see, and if there is a manufacturer name.

Same with the ram memory module you are trying to install.
Also would like to know if the two Foxconn mobos, (MOtherBOard), that I linked above, resemble yours.

Post in a Comment.

I have a Acer Aspire T-180, I added ( 2 ) Crucial 1gb memory sticks, a matched set purchased together. After a while the PC started shutting off, finally got so bad couldn't use the pc. read this email thread and removed the two Crucial memory sticks and I have the pc up and working.
Hard to believe I know, I had Crucial do a check of the pc before buying their recommended memory sticks, I guess it was just too much memory for the pc.

Hi it does not matter what motherboard you have ,its the ram modules your trying to put in thats the problem,go to www.cucial.com and download there crucial system scanner tool and that will tell you the type of memory you have and what type to use.