wierdest booting , software error or hardware ????

Try this first. Boot in safe mode and make sure you have the latest video driver installed if not install the latest.

Already tried , i have the latest driver for graphic card

k, so, in safe boot everything is default, I suggest you do the same, look for a restore point if you have. What windows do you have?

I already did the restore point thing but nothing works out I was using the windows 7 64bit version but yesterday i changed that to windows 10 , i thought windows might be creating the problem ,but its not

The main problem which is making me worry is that why the time taken between from hitting the power button to getting brand logo screen is sooo much increased At normal conditions it takes not more than a second but now its about 5 second This never happened earlier

K, remove the hdd see of it makes any difference in how the laptop boots up. Try to use one of this to have a windows. Also try to run a memtest see what you get.

I did the memtest but its shows no error and removing the hdd also did not work But thankx for your suggestion

Try to get into BIOS and load default values. See if it makes any difference.

If it was oK until you loaded windows 10 then its possible windows 10 has replaced the graphics driver.

I would try re downloading and reinstalling the graphics driver (rather than trying to update the driver in device manager).

Also the time taken between the hitting the power on button to getting the brand name is also extended

I don't think the driver is at fault.

What sort of BIOS is it? possibly Fast Boot needs enabling.

Enable or Disable Fast Boot in UEFI click here