I don't know Bullguard, so my apologies if it is a security suite that includes anti-virus and anti-malware.

Whatever you use, I would download, install, update and run full scans with two other utilities, Malwarebytes' Anti-malware, and SUPERAntispyware.

I don't know Chrome very well, but with both IE and Firefox, there are add-ons that can slow browser speed down, so that's another avenue you could try, an add-on elimination test on each browser.

When you check the Task Manager > Processes tab, click the CPU column header to organise the processes in order of CPU usage. Don't forget the option at the bottom of the screen to show processes from all users.

Are any particular processes using up a lot of CPU time? Disregard the "System Idle" process. If it is above 90% then that is normal.