If you're moving above a certain speed, it won't let you downshift into 1st. Can you go into first from a stop? I never go into first unless I am starting from a stop. Most cars won't let you anyway.

Without knowing the year/make/model and transmission type I can't make a detailed suggestion

it might be time to buy a new clutch

I sa a blog post on this the other day, give me 5 min to check browser history.

um? press the clutch harder? that or ther eis mechanical issues you need to get checked out