My MacBook Pro will not come on. The screen just flashes. Can it be a problem with the battery?
Could be. Start with If your Mac battery won't charge - Apple Support.
If it still will not turn on, proceed with If your Mac doesn't turn on.
Read and follow each of its steps, including all the links within it, all the way through and including Step 4, which directs you to:
If your Mac starts up to a blank screen
Read and follow each of it steps also, all the way through and including the end, which takes you to:
"If you still need help, please contact Apple Support."