4GB DB is cause my server to crash, what should I do ?

[mickeyz]

My server:
Q9550
4GB RAM
500GBX2 WD BLACK

Hi, my server stopped working because of my DB which is bigger then 4GB.
I tried to add another 4GB of RAM (8GB TOTAL) and it didn't work.
I tried to put new Hard Drive but still - didn't work.
I have 8 Million Messages in my forum and don't want to delete them.
What is the problem ? the CPU ? what should I do ?
My server owner told me to delete massages, do I have another solution ?

Thanks !