fluctuating download speeds

Recently I cracked the screen of my Acer aspire V5-571pg laptop and got it repaired by curry's "knowhow" service as it was still under warranty. It was after I got my computer back that my download speeds began to slow or fluctuate considerably. Going from an ~50Mbps connection to 1-3Mbps. Initially I thought it was just a problem with my virgin media connection but after it kept happening a ran a speed test on an older toshiba which gave a clear and consistent ~50Mbps. I have no idea how replacing a screen could cause this but i find it an odd coincidence. Nonetheless the 1-3Mbps speeds made the computer almost unusable for me so, at the advice of curry's staff, i tried a "refresh". This seemed to solve the problem temporarily but my download speeds still fluctuate wildly, ranging from 20-50 which is fine for browsing but not for playing online games and streaming.

I've made sure my network adapter's driver is up to date and run a virus scan (with avast free antivirus) as well as ccleaner to clear out any temporary files.

the two attached files are of the two speed tests one on my acer and one on the toshiba (both images in each attachment are of the same test, with one for the graph to illustrate what i mean by fluctuations) both tests were done on the same network within a minute or so of each other. The tests were done using www.speedtest.net

My computer's specs are:-
Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 8.1, 64 bit
Processor: Intel(R) Core(TM) i5-3337U CPU @ 1.80GHz, Intel64 Family 6 Model 58 Stepping 9
Processor Count: 4
RAM: 7987 Mb
Graphics Card: Intel(R) HD Graphics 4000, -1920 Mb
Hard Drives: C: Total - 938337 MB, Free - 388242 MB;
Motherboard: Acer, Aspire V5-571PG
Antivirus: Windows Defender, Disabled

Any help would be really appreciated, thanks

Attached Thumbnails