very slow while starting

It sounds like you need to do some TLC on your drive:

• Start off by making a good backup of your stuff.
• Using an external bootable drive run Disk Utility from it to make sure the drive is in good shape.
• You'll need to clean off at least of 1/4 of the drive (the more the better) of old documents and apps.
• Next we want to get rid of the old cache & log files using an app like this: Disk Doctor
• Last step! Run a drive defrag program like this if you have a HD (not SSD): Drive Genius

Other things that can help is add more RAM if you can with your system. If you have a traditional HD consider upgrading it to a hybrid (SSHD) like this one: Seagate FireCuda but be careful here as these drives only work in SATA III (6.0 Gb/s) systems if you have an older SATA II (3.0 Gb/s) you'll need the older series. The other option is to upgrade to a SSD drive like this one: Samsung 750 EVO SSD which will work in either a SATA II or SATA III system but the larger drives do get a bit costly so make sure its a wise investment given the age of your system.