when i install 3gb ram in my pc with windows 7 ultimate 32 bit then my pc shows blue screen...help me plz

Did you install the correct specification RAM for your motherboard?

If you don't know, please post full system specification, particularly the motherboard make & exact model.

Also state if you are getting unusual BIOS beeps, and if so state the beep pattern. (long beeps, short beeps, sequence, and how many).

 
Upgrading to 64-bit Windows won't make any difference since the board supports only 2 GB RAM maximum, regardless of the Windows version. It's a hardware limitation of the RAM slots on that board, nothing to do with software.

Zebronics ZEB-945 Motherboard:

RAM : Maximum 2GB DDR2 SDRAM 667/533/400 MHz

If you want more than 2 GB RAM you will have to change the motherboard.