now i got the exact reason y gmail wasnt opening. the date on my PC was set to year 2002. I couldnt change the time and date bcoz of a damaged timedate.cpl. since gmail's current security certificate hadnt been issued in the year 2002, safari was blockin it thinking it was a fake. opera gave me a choice whether i wanted to accept the certificate or not. that's y i was able to open it in opera. now i have replaced timedate.cpl and have set the correct time and date. i can now open gmail in all browsers including safari.