Your system meets the minimum requirements for Windows 7 x86.
Increasing your memory would help, but that will be tempory too if there is an underlying problem.
Specific operating environment would help. Could you provide output from System Information (msinfo32.exe) and export it to text. When you post the sysinfo, please click on the #
sign next to the youtube icon, and paste the report in between the code labels
This is what the text will look like
it makes it easier to scroll through the report.
I'm not sure why performance denegrates over such a short time period, but there are some very good tutorials on this site. See if any in the Performance and Maintenance
section help you. This tutorial
in particular might be where you want to start.