Reasons for low performance in Dell laptop

[mini_04]

Hi,
I am using DELL Inspiron laptop,OS is Windows 7.It was working well.But now few days its performance is very low.Very often I get a warning "Your performance is low", and it shows a message ,"Do you want to change the color scheme to improve performance.
Two options are shown:
1.Existing color scheme
2.Windows basic 7.0 color scheme
If I click the second option " Windows basic 7.0 color scheme",perfromance is improved.
Sometimes when I switch on my laptop,I could hear a small sound.
Please help me ...
By,
Mini

 

[C12Friedman]

Two possibilities come to mind off hand, dust has collected in the heatsink area and you are experiencing thermal throttling or you have some kind of malware running around your OS. This link should help if malware is the issue http://www.tomshardware.com/forum/8263-63-simple-free-guide-removing-malware
Blowing air through the vents may help free dust from the heatsink, I will also suggest using a cooling pad
Hope it helps some