My computer (dell latitude D600) developed a critical problem now. it took longer hour to boost or starting button is not responding quickly. what can i do?

Try uninstalling a few unnecessary programs then click start run type cmd then type chkdsk/r/f this should schedule to happen on reboot which will scan for and attempt to recover bad sectors and automatically fix any corrupt files on your hard drive or
click startcontrol panel administrive tools,computer management ,disk management right click on your drive select properties click tools you should see click check now click start two boxes automatically fix files and scan for and attempt recovery of bad sectors place then a tick in both boxes then select check now,start should schedule this task when restart
do not do anything while the chkdsk utility is in progress any input may damage your computer
then you should test or replace all leads make sure they are securely seated and are not bad/faulty that are attached to your (((motherboard to your hard drive)))
then click start all programs accessories system tools defragment your hard drive
you might have to install more RAM random access memory to check how much ram you have
to check the details on your computer
click start all programs accessories system tools system imformation all of your computer imformation will be there
or click start right click on my computer select properties you will see all imformation about your computer including installed ram
scroll to the bottom toolbar (bottom of screen) right click you can select task manager applications also processes you will see whats running on your computer you might have virus slowing your computer also select users you will see who is using your computer
hope this helps