Ram memory failure critical error

My pc requires some sort of ICU treatments as for last few days everything inside the computer is complaining about problems.
I tried a software System Defragmenter, but that requires purchasing which is not possible in my case.
Now my hardware is started getting corrupt. My hard disk and RAM are somewhat near to die. The latest error I got is

Critical Error RAM memory usage is critically high. RAM memory failure
The pc is Pentium III 933 MHz with 512 mb of RAM and 120 gb hard disk.
As I purchased it one and half year ago, that’s why it is not in any kind of warranty.
I am also low at the budget side, and pc is very essential for me to complete my college assignments.
Does some body have any idea or software that can recover those errors.
If so, do share it with me.
