|Leave Prefetch alone - it is there to speed the start of programs when called. |
See the item "Prefetch folder cleaning" here:
Prefetch does NOT load up redundant items - they are ignored. When the prefetch folder has 132 items Windows reduces the list to 32 (before new startup additions) leaving only the latest. This usually happens every few days, depending upon usage. There is a risk associated with deleting the contents of the complete folder because the file layout.ini has been known to fail to rebuild, which can slow the start of all programs forever unless rebuilt manually.
The only "marginal" case I can see for deleting old prefetch items (but certainly not all of them) is that it makes room for as many as possible until 132 is reached. However, it doesn't seem worth spending time trying to shave off a second or so on their startups when Windows prunes prefetch regularly anyway.
It's worth checking for Malware and Viruses. Try the MalwareBytes freebie which is easy to use and good at unearthing some that AV's can miss.
Uninstall disused background programs. Sometime there is a facility within a program to opt for a manual start - worth considering where practicable. If there is no such facility, type msconfig in the Run box and disable the relevant items in the Startup tab. Strictly msconfig is for diagnostics but it causes no issues when used this way. It can sometimes give you an idea what is causing the problem.
Task Manager (Ctrl-Alt-Del) can might also give a clue about what is overpowering your machine - see Process tab. Be aware that every icon showing next to the clock is a running process. Running a program such as CCleaner Lite (free) and defragmenting the HD might help the machine a little too.