Crash message????

There is no need to worry,it usually happens....!! 

This might be due to you low RAM or CPU capability and you putting much more pressure(read multi tasking) than it is able to handle. Consider opening lesser windows or underatking tasks which consume less resources. If you are using mozilla firefox or internet explorer,change it to chrome. Chrome doesnt crash as much. Also keep ur Cache cleaned. This is no virus just a hiccup of using pc. 
Power fluctuation doesnt affect pc provided PC is connected to UPS. If not,power fluctuation will pose serious threat to your pc components. 

As for unauthorised downloads,keep track of them by regularly scanning through programs installed in control panel

THANKS MOHD AND GOPAL

But im getting crashes even in chrome for many times even while typing this reply also .........and moreover im not using firefox or explorer

it became very disturbance to me

 and im using a laptop not pc , so i think thre is no use with ups na...

my system config is 4gb ram with 750gb hd, and i3 processor 

make sure your pop-up is blocked.

get your laptop to a technical expert

Go into BIOS setup and check ur voltages (even tho its a laptop). my pc had the same problem. u should also check for system conflicts, any new hardware that u might have installed. also check ur RAM & Hard Drive for bad sectors. I can assure you in most likelihood its the last one. For checking ur RAM u can use MEMTEST and for ur hard drive use the software provided by the maufacturer. if it is in warranty contact service, if u have purchased it recently ask for replacement, I say so bcoz if a new thing creates such troubles, god knows knows how much trouble it is going to create when it is old.

Hope this helps

Do only web-browser crashes or whole system ?

If it is only web-browser, there can be many a reasons for that.

1.   Flash Players, Install latest Flash from Adobe.

2.   Some time a badly written web site leads to crash. i.e

      a. Unlimited Loops.

      b. Infinite use of i frames.

      c. Some time N numbers of Browser windows are opened by scriptts.

3.  Some time the Anti-Virus Hoggs the CPU , so much so that the resources available to web-browser is scarce. But as you said you got i3, this might be not the real problem.

4.   Some time you open many browser windows, that leads to crashes. Anything around 200-500 web pages on your system should not crash your system. So I think that is well above the number of pages you open.

5.  Make a habit to clean your /tmp folder time to time, for that you can use CCleaner software.

6.   May be some VIRUS may have crept into your system, and that is causing the problem. So solution to this could be install a software called, DEEP FREEZ, what this software does is, after you finish installing OS and all necessary supporting software, like MS Office, PDF Reader etc..., Install DEEP FREEZ, after the installation of DEEP FREEZ, every time you shut down your system and restart again, it will bring your system to same state, what it was when you installed DEEP FREEZ, by this way no unwanted (VIRUS) sticks to OS, if at all any VIRUS creeps in just reboot the system and lo, it is free of virus.

7.   Above all, use LINUX, any version, please read this : -

"There are about 60,000 viruses known for Windows, 40 or so for the Macintosh, about 5 for commercial Unix versions, and perhaps 40 for Linux. Most of the Windows viruses are not important, but many hundreds have caused widespread damage. Two or three of the Macintosh viruses were widespread enough to be of importance. None of the Unix or Linux viruses became widespread - most were confined to the laboratory."

(Validity of above facts you can verify your self – Just Google it !)

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