Windows 7: Windows 7 - Working fine and slowed down....

Hello,
I am experiencing some performance issues on my PC. First of all, here are the specs:
1. Operating system - Windows 7 Ultimate x64 bit.
2. RAM - 6.00 GB (2.00 + 4.00).
3. Graphics card - AMD ATI Radeon HD 5450.
4. Processor - Intel Dual Core (3.00 GHz).

So here's the problem:
Last week I installed the new 4.00 GB RAM to my PC to make it 6.00 GB. The computer was working fine and everything was all right. Yesterday however, I turned my PC on and inserted my pen drive and transferred a .midi file which I played on my Yamaha PSR-S910 to the computer. When I was doing this I noticed that my PC was usually slow.

Next I quickly scanned my computer with the antivirus (I have Trend Micro Titanium) and I downloaded IOBIT advanced system care and did a full fix.

Now, the computer is a very little bit faster but it gives a lot of problems. Please tell me how I can get my old PC speed back...

IOBIT Smart RAM says the CPU usage is 100%! This is very bad (I think).

Work through these Troubleshooting Steps for Windows 7.

Ok well firstly I would try to remove that 2 GB on ram that you've put on your system. That may be slowing down the computer because as I see you don't have a high end CPU.
Second remove TrendMicro and install a real antivirus like Kaspersky or ESET and do a full scan.
Open up TaskManager and check what programs are running and check CPU usage.
If nothing works do a system restore to a previous saved point.
If problem still occurs then your hardware is to blame.