defragmentation error

my system is very slow so . i checked for spyware malware and viruses but every thing is clean . then i used clean up disk space option to free unwanted space occupied finally i tried disk defragmentation
it says "Disk defragmentation cannot start because the task scheduler is not running " when i click on task schedular it says "Remote Computer Not Found" then i tried to start TASK SCHEDULER From SERVICES but Stat option BOX is disable please kindly somebody help me . My SYSTEM IS DAMM SLOW .i use win 7 os , inspiron 580s . please some body help me to speed up my computer .

Have you tried Microsoft Fixit?
Microsoft Fix it Solution Center: troubleshooting software issues

also try sfc /scannow to correct the system files(you need the Windows 7 installation dvd).
SFC /SCANNOW Command - System File Checker

Fleur chocolat

-Click Start, Run, Type temp and delete everything in this folder
Click Start> |Run| Type msconfig > Enter > Start Up. Uncheck the boxes for the programs that you think you may not use often.
- Run disk clean up (start > programs > accessories > system tools > disk cleanup.)
-Disable background services
- Click Start, In the search bar type "Disk Defragmenter" run the program and make sure all your files are defragmented
-Registry have a great impact on performance of your PC too so always clean your registry
-Use well known antivirus