Screen Lag, Please Help

[Labrynthian]

Hey, so my office laptop is the only laptop I have right now. It's a HP G42 Notebook. I only play DOTA on it, and whenever I play, the screen lags randomly for a solid 4-6 seconds, making it impossible to play properly. I have no idea why this is happening, and I've altered everything I could think of, from resolution and video settings to custom display settings and refresh rate. I've tried really hard to solve the problem, but no matter what I do, it still lags, even when I switch from 1366x768 res to 800x600 res...
Please help, I have no idea what's wrong. It's a 2009 PC with an i3 processor, with specs that really shouldn't have a problem running a 2003 game... please let me know how to resolve this.

Here are the relevant computer specs:

Model: HP G42 Notebook PC
Processor: Intel Core i3 M 370 @ 2.40GHz
RAM: 4GB (2.93GB usable)
System type: 32-bit Operating System
OS: Windows 7 Professional
DirectX Version: DirectX 11
GPU: 1GB Intel HD Graphics card for Core i3
Display: 1366x768 (32 bit) (60Hz refresh rate)

While playing i've checked the task manager and looked at the cpu usage, it's around 33%, which really shouldn't be causing problems, as well as the background programs that are running, and none of them are using much memory, they're just small stuff like explorer.exe etc.

HELP PLEASE

 

[Amartya]

Update graphics driver

 

[Labrynthian]

Update graphics driver

It's up to date...

 

[Amartya]

Then reduce the settings a bit for your game

 

[Labrynthian]

I did... It's a 2003 game running on a 2009 laptop. There shouldn't be a problem at all...

 

[smorizio]

update your network and wifi drivers. if your using wifi conenction see if there any lag using wired. with any pc make sure there no malware or viruses on it. run a malware scan and make sure your anti virus is up to date. micro soft/avg/avast and a few other have free anti virus software. check with the model number on the bottom of the laptop. see if it has just the intel chipset for video or amd/nvidia. if it has a gpu check in the bios that the gpu is turned on and power savings is turned off. use gpu-z to read what video card is active.