Hi Katie,
I'm going to assume that you bought this directly from Dell? If so, it's not acceptable at all in my book - the original laptop would be covered for at least two years under EU regulations. Link to the legislation:
SCADPlus: Sale of consumer goods and associated guarantees
And the important text:
The seller is liable to the consumer for any lack of conformity which exists when the goods are delivered to the consumer and which becomes apparent within a period of two years
Of course, you are also protected by the Sales of Goods Act, which has even longer periods of protection (see
here for some information). It's quite obvious that a laptop is expected to last more than a year (I'm typing this from a Dell laptop I bought just two months ago, I very much hope that it lasts at least six years like my last one!!)
You need to speak to someone higher up - having dealt with Dell I appreciate that they have what I can only politely refer to as foreign call centres, and therefore many of their employees will just be working off of a script.