29.9% APR isn't a particularly high rate of interest, Berti. I've got a credit card which charges rather more than that (and the doorstep lender, Provident, currently charges 272.2% APR).
You've gone past the point (which normally only lasts for a very short while) where you would be entitled to a refund. You're now at the point where the vendor is obliged to repair or replace the laptop. You're entitled to state which of those two options you'd prefer but Brighthouse are entitled to reject your choice if it's not economically viable.
Replacing a hard drive in a desktop PC, and reloading Windows plus the relevant software, would take 'Joe Bloggs' only a few hours. 'Joe Bloggs' might take longer to do the job on a laptop, because of the problems associated with getting inside it, but the manufacturer should be able to tackle a laptop just as quickly as a desktop PC. If the repairer was to attempt to recover your data from the old drive, and to copy it to the new one, it might add an hour or two to the total time but a repair should still take well under a day. Even allowing for the time taken to get the laptop to and from Acer's repair centre, it's hard to see how a repair should take much longer than a week.
Brighthouse are obliged to minimise any inconvenience to you and to ensure that you're not out of pocket as a result of the fault. (If you had to pay for petrol or public transport costs to get the laptop back to Brighthouse and to collect it again, they should refund your expenses). Further, if they're able to provide you with a laptop on loan, they should do so without charge.
For further advice, contact Consumer Direct:
http://www.consumerdirect.gov.uk/contact
Chris