Seven beeps when turned on, but sometimes starts properly

When a laptop or computer first powers on, it goes through an initial set of diagnostic tests to make sure everything under the hood is working properly. These tests are called POST (Power On Self Test). When a test fails, the user is notified via POST codes which can be lights or beeps. 7 beeps are used to indicate a CPU Cache test failure. This can be a processor failure or motherboard failure. For this I would suggest you reseat or replace the CPU/motherboard. You can find a replacement part here.