System doesn"t recognize all my memory, bad bays?

[Guest]

I just tried to upgrade memory, 4 1gb modules. system only recognizes 1gb of memory. Even in bios, 1-3 memory bank shows "not installed" I put back in the original modules, and now it says the same thing, memory bank 4 is the only one that shows installed, even though I am back to the same modules that I have used for two years. HP pavillion a1720n vista home premium 32-bit and with dual boot, windows 7 all worked well until I tried to upgrade memory. any thoughts??? installed crucial recommended ram

 

[GhislainG]

Check for dust in the slots or modules that are not fully inserted.