Finally, put the case back together and test.
When Windows starts, login.
Then click Start, and right-click on My Computer
The screen should say you have xxxMB of RAM, where xxx is the total installed. However, if your graphics card is built into the Motherboard, then the amount of RAM showing may be less - usually 32MB, 64MB or 128MB less.
This screen shows 2.00 GB of RAM