Why Has My Laptop Become Extremely Slow After Installing Bit Defender Internet Security 2013

Configuration:

Processor: i7-2670QM 2.2 GHz

Ram: 8GB DDR3 1333MHz

HDD: 750 GB SATA @ 5400 RPM

Graphics Card: Switchable..1. Intel HD 3000 & 2. ATI HD 6770M - 2 GB DDR5

Operating System: Windows 7 Home Premium 64 Bit (SP1)

I was using Avira Internet Security 2013 until last week when the license expired. Then I got Bit Defender Internet Security 2013 from MakeUseOf.

After installing, my laptop has become extremely slow. Everything is working like tortoise, whether it’s startup or shutdown. If I want to open any program or use MS Office, I have to wait a long time. Half of the time the laptop freezes. It takes a lot of time to scan even I insert an empty pen drive. Everything is just working like slow motion movie.

There is no virus in my PC, I have checked that. Neither I use two antivirus. Is it normal that Bit Defender slows down the PC so much or there is a problem with my laptop?

Really confused as when I was using Avira it was blazing fast.

Please help.

Thanks.