My system keeps crashing

[dbyrns]

Since putting on showtime my system crashes on a almost regular basis. It starts fine, then after a while, although some times it doesn't, it goes to a blue screen
 and says:

driver_IRQL_not less_or_equal

technical:

Stop : 0x000000D1 (0x000000AC, 0x0000007, 0x00000000) 0x994DEA18

nvlddmkm.sys -address 994 dea18 base at 9942c0001, datestamp 4f4e6797

after this shows, i am unable to restart so I have to push the power button to turn it off so I can get it working again. I ran a
 PC doctor diagnostic and systm siagnostic and  everthing passed.

do I need more ram maybe? I have 3 gigs but it can max at 4 gigs, this is the upgrade info for memory:

Dual channel memory architecture

Two 240-pin DDR2 DIMM sockets

Supported DIMM types:

PC2-4200 (533 MHz)

PC2-5300 (667 MHz)

PC2-6400 (800 MHz)

Non-ECC memory only, unbuffered

Supports 2GB DDR2 DIMMs

Supports up to 4 GB*

32 bit PCs cannot address a full 4.0 GB of memory

My system is:

Compaq presario SR5710Y running windows 7 did have vista but up graded.
amd athlon x2 4450e duel processor 2.3 ghz
3 gigs of ram
250gigs of HDD
EVGA pci ex 2.0 geforce gt 520 with 2gb ddr3 memory

could the ddr3 ram on the video car mixed with ddr2 system ram be conflicting?

[Carl]

Well, I hope this works... nvlddmkm.sys causing crashes is related to your graphics card. The file itself is one of the files in the Nvidia driver package. I would follow the instructions you can find on this page. There are some programs listed that can help you with removing your current drivers. Here's the Nvida site's driver download section. Use the fields and it will pick the appropriate driver, save that to your PC and commence cleaning! It's possible something got corrupted, or your current driver version doesn't play nicely with the current version of Sims 3.