Minecraft is Really laggy

Added (1). I'v recently bought a computer of a mate and i can't play minecraft without lagging(5/10 fps)! I have installed optifine and optimized the settings but to no avail. How can i stop minecraft lagging?
Processor: Intel(R) Pentium(R) D CPU 3.00GHz 3.00GHz
RAM:3.50GB (3.22gb usable)
System Type: 64-bit
Graphics Card: ATI RADEON XPRESS 200 Series
Any help would be greatly appreciated, Thanks.

Brook 05.12.2017

Your RAM seems to be the biggest issue there. Minecraft uses Java which is very RAM intensive. You'd need to dedicate around 4GB to Minecraft for it to run well, you can't do that as you only have 4GB of RAM, you can't dedicate it all so it is using very little.

Guest 05.12.2017