Slow PC, Cant uninstall and other issues

Hello and good day.

I just received this computer from my boss. But the computer has lots of problem. Slower speed, some suspicious malware and virus activities, unable to uninstall certain program/software, unable to launch the google chrome and many more. This pc will be use by me only at my workstation.

For your info, I followed your instructions regarding downloading the dds.scr and gmer.zip. I have no problem downloading the dds.scr. However I am unable to download the gmer.zip. It keeps saying that the gmer website is unavailable. Please advice me on what to do.

For your information, my computer details is as below:
Windows XP SP3
512 RAM
80 GB Harddisk
Antivirus: Microsoft Security Essentials.

Thank you.