My computer was running perfectly fine about a week ago,but now its become 100% slower! I got Norton Internet Security 2009 and Spyware Doctor and used them both to scan my computer, solved a few viruses and that was it. I have no new programs installed,in fact, I'd removed some programs. (except for NIS 2009/Spyware Doctor(It was also slow before I got those)) It was still slow...it takes literally about a minute to open programs and about 5 minutes just to start up. Normally it would take 1-2 seconds to open programs and 2 minutes to start up. I really have no clue what to do right now and this is really piddling me off right now!
Can someone PLEASE help me?
Can someone PLEASE help me?

My Computer
System One
-
- Manufacturer/Model
- Gateway DX4860
- CPU
- Intel Core i5-2320 @ 3.00GHz
- Memory
- 6GB DDR3 SDRAM
- Graphics card(s)
- Zotac GeForce GT 240 1GB GDDR5
- Sound Card
- Intel H67 Express
- Monitor(s) Displays
- Samsung SyncMaster 2253LW
- Screen Resolution
- 1680x1050 @ 60Hz
- Hard Drives
- SATA II 1.5TB Hard Drive
- PSU
- 450 Watts
- Mouse
- NexxTech Wired Optical Mouse
- Keyboard
- HP 5189
- Internet Speed
- Telus High Speed 15mb/s