If this is running a 32 bit OS there are instances that having more than 4GB can cause issues in some machines.
Try the usual cleaning with the canned air (see the internet) and if that doesn't help, replace all thermal compounds.
http://h18000.www1.hp.com/products/quickspecs/12577_na/12577_na.PDF shows it has PCIe slots so if this was mine, AFTER I COMPLETED MY REPAIRS (noted in the prior 2 sentences) I would consider the 6670 video card noted at http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107.html
Bob
hi,
I need to upgrade my pc because it is getting really annoying when im playing a game then all of a sudden, bam blue screen.
I have been told its probably my video card and looking online has just confused me. =D
It is at least 4 years old as i got it second hand .
I have:
Mainboard : HP ML110 G4
Chipset : Intel i3000
Processor : Intel Xeon 3040 @ 1866 MHz
Physical Memory : 3072 MB DDR2-SDRAM (i have 5gb in but only 3 showing up)
Video Card : NVIDIA GeForce 9300 GE
Hard Disk : Maxtor 4R160L0 ATA Device (164GB)
DVD-Rom Drive : SONY DVD RW AW-G170A
I would like to add part by part to it, not just buy a whole new PC.
At the moment i only have £150 to upgrade.
What would you guys recommend i buy first?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic