Hi
I have installed linux(ubuntu 11.04) on my dell inspiron 1525.... I has been 4 days and my computer became hang for more than 7 times...

when i close the lid and open i find it in hanged state...... Somebody suggested me to disable the screen saver and i tried it as well but i was unsuccessful...

I re installed ubuntu but also the problem was not solved...,

What should i have to do.. any suggestions?

From what you say it sounds like the notebook is not coming back from sleep. That would be an acpi problem. Research acpi on dell inspiron 1525 and see what others may have done to solve the problem.
Does that mean no video after wake up? Or no keyboard-mouse?
It may be a video driver, keyboard, mouse not coming back after sleep.
You may be able to reload them upon resuming.
Or you may not solve the acpi issue.
Post back if you find the answer, so others can benefit.

http://en.wikipedia.org/wiki/Acpi

This is a common thing on notebooks with intigrated graphics, especially Radeon and Intel brands. I believe it is a firmware issue. The drivers are a part of the Linux kernel and are already installed in the system, the firmware is necessary for the driver to communicate with the hardware, and is non-free (as in free speach), but can be downloaded (I don't remember where from). I have this problem on my 8 year old Dell Latitude C640 with every distro except openSUSE, and Novell is rather cavalier with incorporating non-free software/firmware.