This is my first experience with UBUNTU .i have installed the OS yesterday with Windows 7 and The OS was working well but subsequent using the OS i felt that it was hanging frequently and i had no other option but to reboot the lappy. iam using DELL Inspiron lap.
Ubuntu can theoretically hang on any hardware. I recommend running updates if you're able to use Ubuntu long enough before it freezes, that's the most important thing to do if you are able to. If it hangs immediately after login, was the install really successful in the first place? You can swap the hard drive into another computer and try booting Ubuntu off that hard drive in another machine, that will help you isolate the problem.
When it hangs, if it's from overheating, I highly recommend switching to Lubuntu, which uses LXDE as the desktop environment. I've got much more mileage with Lubuntu on laptops that overheat.
Also consider what kind of graphics card you have. Are you able to do Ctrl+Alt+F1 to swap from GUI to a CLI? This may prevent you from having to reboot your machine by allowing you to enter commands, for instance a