i have a core duo 3.4Ghz Intel processor, its temp. is 55 Celsius degrees, is it ok?

Answer 1

55c = 131 F
when we build the chips we stress em for 125C (257F)
so, you're well within range.

Answer 2

You probably have a Pentium D945 D950 or EE 3.4G because there is no Core2Duo at 3.4Ghz unless overclocked. The max case temps for these Pentiums is 64 to 68°C, so you are nowhere near the danger zone.

However, if that 55°C reading is at idle, I would be alarmed. I would improve case airflow by adding or replacing the case fans w/ better ones and replace the processor heatsink with a Thermalright Ultra 90 or 120.