Carol try
http://support.kaspersky.co.uk/8366
as a first port of call. You have already used the uninstall tool in the software but as you have found that can fail.
On both Mac & PC incomplete AV remvoval is a pain and there is an abundance of specialist removal tools and step by step instructions for all such.
If you Google "Kaspersky removal tool" I'm sure you will find a solution.
I would also try re-installing Kaspersky if allowed and then uninstalling. That may work occasionally if some incomplete removal has left a corrupt installation.
Only a couple of days ago I tried to remove Microsoft Security Essentials from a PC for a friend and neither was it running or indeed removable or reinstallable. In fact there was a virus preventing such. It needed removing with some other tools first before installing AVG as replacement protection.
As for AVAST. Some people swear by it and others at it. I found on some PCs it would cause the PC to run slow as it clashed with other parts of the OS.
I am not too familiar with MAC software but the principles are the same. There will be an additional removal tool and or detailed manual instructions for removal. Just a matter of using Google to find them.
Try the re-install/uninstall route first. Then have a look at http://www.filehippo.com and see what Malware removal tools are available to check whether you have a virus which as pointed out is a possibility. Most are very secretive these days until you rattle their cage as they often disable or corrupt AV software to do their work.
I must say there seems generally to be an increase in virus activity in the last months. I seem to have removed ransom ware at least 4 or 5 times in the last month from various PCs.
Don't know off hand whether AVG (free) is available on a MAC but fairly sure it is. I wouldn't have recommended it at all a few years back but it is much improved and I have moved all my PCs etc to use that only a few weeks ago and it seems pretty good.
Unfortunately there is no such thing as a perfect AV solution and you really need a combination of things these days. I use in addition free versions of Superantispyware, Malware Bytes and Hitman Kickstart as 2nd opinion checks. The latter removed the unknown problem with the compromised MSE the other week.
I would advise anyone using a PC or MAC to get a copy of Hitman Kickstart free and install it on a flash drive as a bootable rescue disc. It does it all for you. Don't run it immediately to check only unless you need to as it gives you 30 days free for removal following registering with an email address.
HTH helps.