I think you must check for the virus in your computer or there will be more files or movies in your c drive in my computer so reduce some of the files in your system will make your system faster.
upgrade your computer.i think your computer has become too much old.you should buy at least core processor with RAM minimum 2GB.
don't not used memory resentment program set the booting programs from registry and also share virtual memory you feel batter..
I have to agree with everyone here, OP. You could get a used computer with much better specs than the one you already have - it's time to upgrade! Have you tried defragging it?
With Processor :- Pentium-4, 1.8 GHz Ram :- 512 MB ,i think you have to upgrade your Memory module From 512 MB to 1024 MB , and protect with antivirus and always update every week to secure your files.with 1024 of memory module it make your computer more faster .
you can download quick heal trial version from quick heal website. trial version is free for 30 days.you can install is after download in your PC. you can scan your PC. or increase 1 GB Ram.