How weird! I just took my PC to a technician today, and my comp shutdown after 30 mins of me using it! It's done it before so then I changed it to windows vista and it was fine. I prefer windows XP tho, but now that I have it again it started shutting down every 30 mins like before!!! Does anyone know what I can do?

Did the technician explain to you what he has done to your computer? More info is need.

There are perhaps two underlying reasons for shut down.
1. obvious but I expect you've checked ALL the deliberate hibernation, sleep, turn off hard disk etc
2. Some component is overheating. it can be as simple as the power supply full of dust, it can be the computer is not getting sufficient ventilation and I have had one where the processor cooling heat sink was full of dirt. Some components have an automatic temperature safeguard and switch off if too hot, then cool and work again for a while. Yours seems to be in this category.

Microsoft Windows is a series of software operating systems and graphical user interfaces produced by Microsoft. Microsoft first introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces (GUIs).[2] Microsoft Windows came to dominate the world's personal computer market, overtaking Mac OS, which had been introduced in 1984. As of October 2009, Windows had approximately 91% of the market share of the client operating systems for usage on the Internet.[3][4][5] The most recent client version of Windows is Windows 7; the most recent server version is Windows Server 2008 R2; the most recent mobile OS version is Windows Phone 7.Homework Help

Gee. You almost totally disguise your advertisement with the potted Microsoft OS history. Almost. I hope your students do not expect tutelage of a high standard of English expression.

There's a setting in XP that will shut your system down to prevent further corruption. You need to use the repair utility while in DOS mode.