Its not always the case, that it will show the whole RAM you have installed is being used by your operating System.
For example, even if you have installed 4 Gb RAM on an 32 Bit Windows 7, it will still show, 2.99 Gb as usable RAM, Because the 32 Bit Operating System is not capable of Handling More RAM, Even if you Install 16 Gb RAM, it will still show you the Same 2.99 Gb RAM.
(P.S. : 64 Bit Windows 7 is capable of Handling about 3.86 Gb RAM.)

If you still think, one of the RAM chip is not Functioning, you can always check, using the System Information utility of Windows Operating System that what is the amount of Installed Physical memory in your Computer.
Open command prompt (Run then type in cmd and press enter)
In command Prompt, type in "systeminfo" and press enter and then satisfy yourself.

* I dont wanna be rude, But...
I Dis-agree with whyme123's First line,
"If your ram chip "Crapped", you wouldn't even be able to boot into windows."

Because, if you have multiple slots for RAM and multiple RAM chip installed in your system, the CPU will not generate the error-code (or Beep alert for RAM) during the POST (Power On Self Test ) even if only a single RAM chip is Functioning properly, rest all got failed, it will ignore the other RAM Chips Failure.
The First line is true, only when it doesn't recognize a single RAM-Chip (No Ram at all).
:(

Hope, it is cleared, Best of Luck.

*Please forgive me for my weak English, Because i 'm not a native speaker of English*

Through Experience.
Electronics Engineer And Tech-Blogger.

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