My lord, they ripped you off.
£500 !! to fix a 7-year-old PC.
For that you could have bought a new gaming screamer.
Last year for $500 Cdn (~ £320), I got a quad-core laptop with 6 GB RAM, 750 GB hard drive, & discrete video processor, plus a wireless keyboard & mouse. They also threw in Windows Office.
Plug it into the big-screen TV & sit in your easy chair.
All the major bits inside: motherboard, RAM, & HD keep getting faster & cheaper, with more capacity, so it doesn't make sense economically to upgrade an old machine.
A symptom of our throw-away society.
I hope the upgrade, or whatever they did, lasts you another 5 years, but doubtful.