The fact that you have very slow start up means that there are numerous programs that automatically loads everytime you start your system. The best thing to do is to get a program that allows you to manage your startup programs and try to disable them. In my case, I usually use advance system care software which is free to download (just google for it).
Aside from that, you may have to defragment your hard disk in order to organize your files and folders. this is one of the admin tools as part of your OS. (program>accessories>system tools>disk defragmenter)
Another option is to clean your registry of junk files. The aforesaid software can also do this part.
Moreover, run an anti-virus scan; your laptop could be infected by an unknown virus.
If all these things failed to resolve the issue then your last resort is to reformat your laptop using the recovery disk that comes along with your purchase