I have been looking at some refurbished pc's on ebay.
The only refurbished PCs worth looking at are almost new (and still current) ones that were fixed after an initial problem. Anything other is likely poor value for money or it's refurbishment is minimal compared to any other second hand machine.
the processor in mine is celeron dual core 1.9ghz
Which one though? Intel have produced Celeron branded processors running at 1.9Ghz since 2002 and as you can imagine they've gotten an awful lot faster over that time.
The reviews for your laptop appear to be for late 2009 so I'm guessing the most likely candidate is the Core 2 based Celeron T3100. I seem to remember they were pretty good processors at the time.
4200rpm, 5400rpm or 7200rpm?
My laptop has ground to a standstill today becuase I had several windows open and needed to keep jumping backwards & forwards. Yet again I needed to reboot before it would wake up.
I need something that is fast at multi-tasking.
I haven't used a low end chip of that era but I'm not convinced it is your problem. I'm writing this on a computer using the same chip design, actually an older revision of it released in 2006, and while it is a higher end chip running at 2.4Ghz with 4MB of cache I've currently got eleven tabs in my web browser and three other windows open without a problem.
Generally if you're grinding completely to a halt that indicates a problem, especially if your cursor is freezing up too, rather than a lack of power. I've just had to wipe someone's computer from 2002 and while that was ludicrously slow with the software that had been put on it recently, it nevertheless always got there eventually. It could be a software problem or it could be hardware failure.
Assuming you've got your stuff backed up you could try a factory reset/windows reinstall and see if that improves the situation any. As that will wipe everything that should solve any software problems.