Post the first third of your dxdiag here. The whole thing won't fit in a single post nor is it all needed. It looks like a resource issue. As you add more enemies, friendlys or sounds your computer is stumbling to keep up.
Approximately the first 1/3 of the txt file:
perating System: Windows 7 Home Premium 64-bit (6.1, Build 7600) (7600.win7_gdr.120830-0334)
Language: English (Regional Setting: English)
System Manufacturer: Hewlett-Packard
System Model: p6537c
BIOS: BIOS Date: 04/22/10 21:35:46 Ver: 6.04
Processor: AMD Phenom(tm) II X4 830 Processor (4 CPUs), ~2.8GHz
Memory: 6144MB RAM
Available OS Memory: 5888MB RAM
Page File: 1642MB used, 10130MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 11
DX Setup Parameters: Not found
User DPI Setting: 144 DPI (150 percent)
System DPI Setting: 96 DPI (100 percent)
DWM DPI Scaling: Enabled
DxDiag Version: 6.01.7600.16385 32bit Unicode
------------
DxDiag Notes
------------
Display Tab 1: No problems found.
Sound Tab 1: No problems found.
Sound Tab 2: No problems found.
Input Tab: No problems found.
--------------------
DirectX Debug Levels
--------------------
Direct3D: 0/4 (retail)
DirectDraw: 0/4 (retail)
DirectInput: 0/5 (retail)
DirectMusic: 0/5 (retail)
DirectPlay: 0/9 (retail)
DirectSound: 0/5 (retail)
DirectShow: 0/6 (retail)
---------------
Display Devices
---------------
Card name: ATI Radeon 3000 Graphics
Manufacturer: ATI Technologies Inc.
Chip type: ATI display adapter (0x9616)
DAC type: Internal DAC(400MHz)
Device Key: Enum\PCI\VEN_1002&DEV_9616&SUBSYS_2AA9103C&REV_00
Display Memory: 2940 MB
Dedicated Memory: 252 MB
Shared Memory: 2687 MB
Current Mode: 1920 x 1080 (32 bit) (59Hz)
Monitor Name: HP 2310 Series Wide LCD Monitor
Monitor Model: HP 2310
Monitor Id: HWP288E
Native Mode: 1920 x 1080(p) (60.000Hz)
Output Type: DVI
Driver Name: aticfx64.dll,aticfx64.dll,aticfx32,aticfx32,atiumd64.dll,atidxx64.dll,atiumdag,atidxx32,atiumdva,atiumd6a.cap,atitmm64.dll
Driver File Version: 8.17.0010.0024 (English)
Driver Version: 8.733.0.0
DDI Version: 10
Driver Model: WDDM 1.1
Driver Attributes: Final Retail
Driver Date/Size: 5/12/2010 02:19:40, 584704 bytes
WHQL Logo'd: Yes
WHQL Date Stamp:
Device Identifier: {D7B71EE2-D556-11CF-9473-A30ABEC2C535}
Vendor ID: 0x1002
Device ID: 0x9616
SubSys ID: 0x2AA9103C
Revision ID: 0x0000
Driver Strong Name: oem61.inf:ATI.Mfg.NTamd64.6.1:ati2mtag_RS780:8.733.0.0:pci\ven_1002&dev_9616&subsys_2aa9103c
Rank Of Driver: 00E60001
Is that enough of dxdiag?Thanks,
Rot