It's hard to find out DDR2 RAM memories nowadays. Moreover, these old ones are doing sold at a very high market price. Can I use a ddr3 ram on a motherboard which originally supports ddr2 on it? If so will there be any future problems?
No, motherboards cannot support both DDR2 and DDR3 RAM. They are different technologies with different pinouts and voltage requirements. Trying to use DDR2 RAM in a DDR3 motherboard or vice versa will not work and could damage the memory or the motherboard.
There are a few motherboards that have both DDR2 and DDR3 slots, but these are rare and are typically designed for use with older systems that have been upgraded with DDR3 memory. If you are unsure whether your motherboard supports DDR2 or DDR3 RAM, you should consult the motherboard's manual.