Any chance you're mining XPM??? With a single core CPU it can almost bring it to a halt.
Did recently install a new wallet and you're downloading its blockchain? That slows my PC down to a snail's pace.
What difficulty have you set? I know with Block Erupters a high difficulty is detrimental. But, my GPU miners don't care what difficulty I set.
Open your Task Manager and see what applications and processes are running. I downloaded a shareware ap the other day and it installed this obnoxious PCBackUp that was grinding away in background. Uninstalling it sped my PC back to normal.
I'm mining whatever the Multipool server has switched to, but XPM isn't one of the coins it deals with. I do have the EMD (Emerald) and BTB (Bitbar) wallet applications but neither are running. I'm not doing any CPU mining, just GPU. The first machine's specs are: QX9650 Core2Quad Extreme, 4GB DDR3-1600, GTX580 running Cudaminer (difficulty 16). The other one's are: Phenom X3 710, 4GB DDR2-800, HD5870 running Reaper (difficulty 32). Both are running their miners via GUIMiner-Scrypt Alpha x0.04. Google Chrome is fully using one processor core on the machine with the GTX580 as this is my main machine, both machines are running HWMonitor to keep an eye on their GPU temperatures, other than that there's not much else running, the HDD is mostly idle and there's plenty of ram free. I set the difficulties as suggested by the Multipool website, I could try raising them, maybe that would cut down on the network traffic.
Cudaminer's batch file that starts it for the GTX580:
"C:\Users\Mickey\Downloads\guiminer-scrypt_win32_binaries_v0.04\cudaminer\cudaminer.exe" -o
http://localhost:8332/ -O MickeyT2008.MLT:1 -d 0 -i 1 -l 32x8 -C 2 -m 1
Reaper.conf from the machine with the HD5870:
kernel reaper.cl
save_binaries yes
enable_graceful_shutdown no
long_polling yes
platform 0
device 0
mine litecoin
And the litecoin.conf file that it uses, I assume that using that is correct with scrypt:
host localhost
port 8332
user MickeyT2008.MLT2
pass [removed]
protocol litecoin
gpu_thread_concurrency 6720
worksize 256
vectors 1
aggression 18
threads_per_gpu 1
sharethreads 32
lookup_gap 2