Random Screen Lag, Please Help

Hey, so the laptop my office provides is a HP G42 Notebook, from 2009. DOTA is the only game I play on it, and for some reason, the screen randomly lags now and then. The screen freezes for a solid 5-6 seconds, while the game continues. It's impossible to play like this, and no matter how much I've tried altering the settings, the lag won't go and I can't understand why. The system specs and GPU should easily be able to handle a 2003 game. Also, when it's not lagging, it works like a dream. I just need to get rid of the random freezing and I'll be set. Please give me ideas, I'm all out...

Here's the necessary computer information:

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)

Please take a look and tell me what I can do to solve this freezing problem. It's just the display, not my internet or anything else.

Thanks