Cannot enable cache

Hello.

Sorry to bother but I have a big problem now, I enabled the mobile tools module and I used the "Switch theme for a mobile device" option, the one that has a little asterisk that tells you it disables cache.

Once I realized that the cache was, in fact, not working, I tried the other options but I still couldn't reenable cache. I ended up uninstalling the module, I deleted all of its files and folder, and I still cannot enable cache.

I choose normal cache, and I save the settings page, I get the usual "Settings have been saved message" but no option is selected, and no matter what I do Normal cache won't get enabled.

Can anyone tell me what mobile tools does to disable the cache and how I can revert it so that cache works again?

Thanks to anyone who can help.