Login problems

I have a few wordpress sites – one of which I have recently purchased. Initially, I changed the admin password and have used it for the past couple weeks, however, yesterday it took many attempts in order to login – I got in once, and can no longer login. I’m not sure what, if anything, I can do. I deleted my cache’s, web-history, cookies etc… tried to login on my desktop at work and couldn’t. IT’s very strange to me, I’ve never seen this happen before. This is essentially a stab in the dark to see if anyone else was having the same problem or has encountered it.
Thanks,
JG